lsp: vim.lsp.diagnostic (#12655)

Breaking Changes:
- Deprecated all `vim.lsp.util.{*diagnostics*}()` functions.
    - Instead, all functions must be found in vim.lsp.diagnostic
    - For now, they issue a warning ONCE per neovim session. In a
      "little while" we will remove them completely.
- `vim.lsp.callbacks` has moved to `vim.lsp.handlers`.
    - For a "little while" we will just redirect `vim.lsp.callbacks` to
      `vim.lsp.handlers`. However, we will remove this at some point, so
      it is recommended that you change all of your references to
      `callbacks` into `handlers`.
    - This also means that for functions like |vim.lsp.start_client()|
      and similar, keyword style arguments have moved from "callbacks"
      to "handlers". Once again, these are currently being forward, but
      will cease to be forwarded in a "little while".
- Changed the highlight groups for LspDiagnostic highlight as they were
  inconsistently named.
    - For more information, see |lsp-highlight-diagnostics|
- Changed the sign group names as well, to be consistent with
  |lsp-highlight-diagnostics|

General Enhancements:
- Rewrote much of the getting started help document for lsp. It also
  provides a much nicer configuration strategy, so as to not recommend
  globally overwriting builtin neovim mappings.

LSP Enhancements:
- Introduced the concept of |lsp-handlers| which will allow much better
  customization for users without having to copy & paste entire files /
  functions / etc.

Diagnostic Enhancements:
- "goto next diagnostic" |vim.lsp.diagnostic.goto_next()|
- "goto prev diagnostic" |vim.lsp.diagnostic.goto_prev()|
    - For each of the gotos, auto open diagnostics is available as a
      configuration option
- Configurable diagnostic handling:
    - See |vim.lsp.diagnostic.on_publish_diagnostics()|
    - Delay display until after insert mode
    - Configure signs
    - Configure virtual text
    - Configure underline
- Set the location list with the buffers diagnostics.
    - See |vim.lsp.diagnostic.set_loclist()|
- Better performance for getting counts and line diagnostics
    - They are now cached on save, to enhance lookups.
    - Particularly useful for checking in statusline, etc.
- Actual testing :)
    - See ./test/functional/plugin/lsp/diagnostic_spec.lua
- Added `guisp` for underline highlighting

NOTE: "a little while" means enough time to feel like most plugins and
plugin authors have had a chance to refactor their code to use the
updated calls. Then we will remove them completely. There is no need to
keep them, because we don't have any released version of neovim that
exposes these APIs. I'm trying to be nice to people following HEAD :)

Co-authored: [Twitch Chat 2020](https://twitch.tv/teej_dv)

11 files changed, 1824 insertions, 796 deletions

diff --git a/runtime/lua/vim/F.lua b/runtime/lua/vim/F.lua
new file mode 100644
index 0000000000..5887e978b9
--- /dev/null
+++ b/runtime/lua/vim/F.lua
@@ -0,0 +1,24 @@
+local F = {}
+
+--- Returns {a} if it is not nil, otherwise returns {b}.
+---
+--@param a
+--@param b
+function F.if_nil(a, b)
+  if a == nil then return b end
+  return a
+end
+
+-- Use in combination with pcall
+function F.ok_or_nil(status, ...)
+  if not status then return end
+  return ...
+end
+
+-- Nil pcall.
+function F.npcall(fn, ...)
+  return F.ok_or_nil(pcall(fn, ...))
+end
+
+
+return F
diff --git a/runtime/lua/vim/highlight.lua b/runtime/lua/vim/highlight.lua
index 705b34dc99..0012dce081 100644
--- a/runtime/lua/vim/highlight.lua
+++ b/runtime/lua/vim/highlight.lua
@@ -2,6 +2,22 @@ local api = vim.api
 
 local highlight = {}
 
+--@private
+function highlight.create(higroup, hi_info, default)
+  local options = {}
+  -- TODO: Add validation
+  for k, v in pairs(hi_info) do
+    table.insert(options, string.format("%s=%s", k, v))
+  end
+  vim.cmd(string.format([[highlight %s %s %s]], default and "default" or "", higroup, table.concat(options, " ")))
+end
+
+--@private
+function highlight.link(higroup, link_to, force)
+  vim.cmd(string.format([[highlight%s link %s %s]], force and "!" or " default", higroup, link_to))
+end
+
+
 --- Highlight range between two positions
 ---
 --@param bufnr number of buffer to apply highlighting to
diff --git a/runtime/lua/vim/lsp.lua b/runtime/lua/vim/lsp.lua
index 1a0015e2db..dacdbcfa17 100644
--- a/runtime/lua/vim/lsp.lua
+++ b/runtime/lua/vim/lsp.lua
@@ -1,4 +1,4 @@
-local default_callbacks = require 'vim.lsp.callbacks'
+local default_handlers = require 'vim.lsp.handlers'
 local log = require 'vim.lsp.log'
 local lsp_rpc = require 'vim.lsp.rpc'
 local protocol = require 'vim.lsp.protocol'
@@ -13,16 +13,21 @@ local validate = vim.validate
 
 local lsp = {
   protocol = protocol;
-  callbacks = default_callbacks;
+
+  -- TODO(tjdevries): Add in the warning that `callbacks` is no longer supported.
+  -- util.warn_once("vim.lsp.callbacks is deprecated. Use vim.lsp.handlers instead.")
+  handlers = default_handlers;
+  callbacks = default_handlers;
+
   buf = require'vim.lsp.buf';
+  diagnostic = require'vim.lsp.diagnostic';
   util = util;
+
   -- Allow raw RPC access.
   rpc = lsp_rpc;
+
   -- Export these directly from rpc.
   rpc_response_error = lsp_rpc.rpc_response_error;
-  -- You probably won't need this directly, since __tostring is set for errors
-  -- by the RPC.
-  -- format_rpc_error = lsp_rpc.format_rpc_error;
 }
 
 -- maps request name to the required resolved_capability in the client.
@@ -72,7 +77,7 @@ local function resolve_bufnr(bufnr)
 end
 
 --@private
---- callback called by the client when trying to call a method that's not
+--- Called by the client when trying to call a method that's not
 --- supported in any of the servers registered for the current buffer.
 --@param method (string) name of the method
 function lsp._unsupported_method(method)
@@ -115,14 +120,14 @@ local all_buffer_active_clients = {}
 local uninitialized_clients = {}
 
 --@private
---- Invokes a callback for each LSP client attached to the buffer {bufnr}.
+--- Invokes a function for each LSP client attached to the buffer {bufnr}.
 ---
 --@param bufnr (Number) of buffer
---@param callback (function({client}, {client_id}, {bufnr}) Function to run on
+--@param fn (function({client}, {client_id}, {bufnr}) Function to run on
 ---each client attached to that buffer.
-local function for_each_buffer_client(bufnr, callback)
+local function for_each_buffer_client(bufnr, fn)
   validate {
-    callback = { callback, 'f' };
+    fn = { fn, 'f' };
   }
   bufnr = resolve_bufnr(bufnr)
   local client_ids = all_buffer_active_clients[bufnr]
@@ -132,7 +137,7 @@ local function for_each_buffer_client(bufnr, callback)
   for client_id in pairs(client_ids) do
     local client = active_clients[client_id]
     if client then
-      callback(client, client_id, bufnr)
+      fn(client, client_id, bufnr)
     end
   end
 end
@@ -209,7 +214,9 @@ local function validate_client_config(config)
   }
   validate {
     root_dir        = { config.root_dir, is_dir, "directory" };
+    -- TODO(remove-callbacks)
     callbacks       = { config.callbacks, "t", true };
+    handlers        = { config.handlers, "t", true };
     capabilities    = { config.capabilities, "t", true };
     cmd_cwd         = { config.cmd_cwd, optional_validator(is_dir), "directory" };
     cmd_env         = { config.cmd_env, "t", true };
@@ -220,13 +227,23 @@ local function validate_client_config(config)
     before_init     = { config.before_init, "f", true };
     offset_encoding = { config.offset_encoding, "s", true };
   }
+
+  -- TODO(remove-callbacks)
+  if config.handlers and config.callbacks then
+    error(debug.traceback(
+      "Unable to configure LSP with both 'config.handlers' and 'config.callbacks'. Use 'config.handlers' exclusively."
+    ))
+  end
+
   local cmd, cmd_args = lsp._cmd_parts(config.cmd)
   local offset_encoding = valid_encodings.UTF16
   if config.offset_encoding then
     offset_encoding = validate_encoding(config.offset_encoding)
   end
+
   return {
-    cmd = cmd; cmd_args = cmd_args;
+    cmd = cmd;
+    cmd_args = cmd_args;
     offset_encoding = offset_encoding;
   }
 end
@@ -276,12 +293,11 @@ end
 ---
 --- - Methods:
 ---
----  - request(method, params, [callback], bufnr)
+---  - request(method, params, [handler], bufnr)
 ---     Sends a request to the server.
 ---     This is a thin wrapper around {client.rpc.request} with some additional
 ---     checking.
----     If {callback} is not specified, it will use {client.callbacks} to try to
----     find a callback. If one is not found there, then an error will occur.
+---     If {handler} is not specified,  If one is not found there, then an error will occur.
 ---     Returns: {status}, {[client_id]}. {status} is a boolean indicating if
 ---     the notification was successful. If it is `false`, then it will always
 ---     be `false` (the client has shutdown).
@@ -325,8 +341,7 @@ end
 ---    with the server. You can modify this in the `config`'s `on_init` method
 ---    before text is sent to the server.
 ---
----  - {callbacks} (table): The callbacks used by the client as
----    described in |lsp-callbacks|.
+---  - {handlers} (table): The handlers used by the client as described in |lsp-handler|.
 ---
 ---  - {config} (table): copy of the table that was passed by the user
 ---    to |vim.lsp.start_client()|.
@@ -378,15 +393,7 @@ end
 ---   `{[vim.type_idx]=vim.types.dictionary}`, else it will be encoded as an
 ---   array.
 ---
---@param callbacks Map of language server method names to
---- `function(err, method, params, client_id)` handler. Invoked for:
---- - Notifications to the server, where `err` will always be `nil`.
---- - Requests by the server. For these you can respond by returning
----   two values: `result, err` where err must be shaped like a RPC error,
----   i.e. `{ code, message, data? }`. Use |vim.lsp.rpc_response_error()| to
----   help with this.
---- - Default callback for client requests not explicitly specifying
----   a callback.
+--@param handlers Map of language server method names to |lsp-handler|
 ---
 --@param init_options Values to pass in the initialization request
 --- as `initializationOptions`. See `initialize` in the LSP spec.
@@ -437,52 +444,51 @@ function lsp.start_client(config)
 
   local client_id = next_client_id()
 
-  local callbacks = config.callbacks or {}
+  -- TODO(remove-callbacks)
+  local handlers = config.handlers or config.callbacks or {}
   local name = config.name or tostring(client_id)
   local log_prefix = string.format("LSP[%s]", name)
 
-  local handlers = {}
+  local dispatch = {}
 
   --@private
-  --- Returns the callback associated with an LSP method. Returns the default
-  --- callback if the user hasn't set a custom one.
+  --- Returns the handler associated with an LSP method.
+  --- Returns the default handler if the user hasn't set a custom one.
   ---
   --@param method (string) LSP method name
-  --@returns (fn) The callback for the given method, if defined, or the default
-  ---from |lsp-callbacks|
-  local function resolve_callback(method)
-    return callbacks[method] or default_callbacks[method]
+  --@returns (fn) The handler for the given method, if defined, or the default from |vim.lsp.handlers|
+  local function resolve_handler(method)
+    return handlers[method] or default_handlers[method]
   end
 
   --@private
   --- Handles a notification sent by an LSP server by invoking the
-  --- corresponding callback.
+  --- corresponding handler.
   ---
   --@param method (string) LSP method name
   --@param params (table) The parameters for that method.
-  function handlers.notification(method, params)
+  function dispatch.notification(method, params)
     local _ = log.debug() and log.debug('notification', method, params)
-    local callback = resolve_callback(method)
-    if callback then
+    local handler = resolve_handler(method)
+    if handler then
       -- Method name is provided here for convenience.
-      callback(nil, method, params, client_id)
+      handler(nil, method, params, client_id)
     end
   end
 
   --@private
-  --- Handles a request from an LSP server by invoking the corresponding
-  --- callback.
+  --- Handles a request from an LSP server by invoking the corresponding handler.
   ---
   --@param method (string) LSP method name
   --@param params (table) The parameters for that method
-  function handlers.server_request(method, params)
+  function dispatch.server_request(method, params)
     local _ = log.debug() and log.debug('server_request', method, params)
-    local callback = resolve_callback(method)
-    if callback then
-      local _ = log.debug() and log.debug("server_request: found callback for", method)
-      return callback(nil, method, params, client_id)
+    local handler = resolve_handler(method)
+    if handler then
+      local _ = log.debug() and log.debug("server_request: found handler for", method)
+      return handler(nil, method, params, client_id)
     end
-    local _ = log.debug() and log.debug("server_request: no callback found for", method)
+    local _ = log.debug() and log.debug("server_request: no handler found for", method)
     return nil, lsp.rpc_response_error(protocol.ErrorCodes.MethodNotFound)
   end
 
@@ -493,7 +499,7 @@ function lsp.start_client(config)
   --@param err (...) Other arguments may be passed depending on the error kind
   --@see |vim.lsp.client_errors| for possible errors. Use
   ---`vim.lsp.client_errors[code]` to get a human-friendly name.
-  function handlers.on_error(code, err)
+  function dispatch.on_error(code, err)
     local _ = log.error() and log.error(log_prefix, "on_error", { code = lsp.client_errors[code], err = err })
     err_message(log_prefix, ': Error ', lsp.client_errors[code], ': ', vim.inspect(err))
     if config.on_error then
@@ -510,7 +516,7 @@ function lsp.start_client(config)
   ---
   --@param code (number) exit code of the process
   --@param signal (number) the signal used to terminate (if any)
-  function handlers.on_exit(code, signal)
+  function dispatch.on_exit(code, signal)
     active_clients[client_id] = nil
     uninitialized_clients[client_id] = nil
     local active_buffers = {}
@@ -523,7 +529,7 @@ function lsp.start_client(config)
     -- Buffer level cleanup
     vim.schedule(function()
       for _, bufnr in ipairs(active_buffers) do
-        util.buf_clear_diagnostics(bufnr)
+        lsp.diagnostic.clear(bufnr)
       end
     end)
     if config.on_exit then
@@ -532,7 +538,7 @@ function lsp.start_client(config)
   end
 
   -- Start the RPC client.
-  local rpc = lsp_rpc.start(cmd, cmd_args, handlers, {
+  local rpc = lsp_rpc.start(cmd, cmd_args, dispatch, {
     cwd = config.cmd_cwd;
     env = config.cmd_env;
   })
@@ -542,12 +548,14 @@ function lsp.start_client(config)
     name = name;
     rpc = rpc;
     offset_encoding = offset_encoding;
-    callbacks = callbacks;
     config = config;
+
+    -- TODO(remove-callbacks)
+    callbacks = handlers;
+    handlers = handlers;
   }
 
-  -- Store the uninitialized_clients for cleanup in case we exit before
-  -- initialize finishes.
+  -- Store the uninitialized_clients for cleanup in case we exit before initialize finishes.
   uninitialized_clients[client_id] = client;
 
   --@private
@@ -641,13 +649,11 @@ function lsp.start_client(config)
   --- Sends a request to the server.
   ---
   --- This is a thin wrapper around {client.rpc.request} with some additional
-  --- checks for capabilities and callback availability.
+  --- checks for capabilities and handler availability.
   ---
   --@param method (string) LSP method name.
   --@param params (table) LSP request params.
-  --@param callback (function, optional) Response handler for this method.
-  ---If {callback} is not specified, it will use {client.callbacks} to try to
-  ---find a callback. If one is not found there, then an error will occur.
+  --@param handler (function, optional) Response |lsp-handler| for this method.
   --@param bufnr (number) Buffer handle (0 for current).
   --@returns ({status}, [request_id]): {status} is a bool indicating
   ---whether the request was successful. If it is `false`, then it will
@@ -656,16 +662,14 @@ function lsp.start_client(config)
   ---second result. You can use this with `client.cancel_request(request_id)`
   ---to cancel the-request.
   --@see |vim.lsp.buf_request()|
-  function client.request(method, params, callback, bufnr)
-    -- FIXME: callback is optional, but bufnr is apparently not? Shouldn't that
-    -- require a `select('#', ...)` call?
-    if not callback then
-      callback = resolve_callback(method)
-        or error(string.format("not found: %q request callback for client %q.", method, client.name))
+  function client.request(method, params, handler, bufnr)
+    if not handler then
+      handler = resolve_handler(method)
+        or error(string.format("not found: %q request handler for client %q.", method, client.name))
     end
-    local _ = log.debug() and log.debug(log_prefix, "client.request", client_id, method, params, callback, bufnr)
+    local _ = log.debug() and log.debug(log_prefix, "client.request", client_id, method, params, handler, bufnr)
     return rpc.request(method, params, function(err, result)
-      callback(err, method, result, client_id, bufnr)
+      handler(err, method, result, client_id, bufnr)
     end)
   end
 
@@ -995,19 +999,18 @@ nvim_command("autocmd VimLeavePre * lua vim.lsp._vim_exit_handler()")
 --@param bufnr (number) Buffer handle, or 0 for current.
 --@param method (string) LSP method name
 --@param params (optional, table) Parameters to send to the server
---@param callback (optional, functionnil) Handler
---  `function(err, method, params, client_id)` for this request. Defaults
---  to the client callback in `client.callbacks`. See |lsp-callbacks|.
+--@param handler (optional, function) See |lsp-handler|
+--  If nil, follows resolution strategy defined in |lsp-handler-configuration|
 --
 --@returns 2-tuple:
 ---  - Map of client-id:request-id pairs for all successful requests.
 ---  - Function which can be used to cancel all the requests. You could instead
 ---    iterate all clients and call their `cancel_request()` methods.
-function lsp.buf_request(bufnr, method, params, callback)
+function lsp.buf_request(bufnr, method, params, handler)
   validate {
     bufnr    = { bufnr, 'n', true };
     method   = { method, 's' };
-    callback = { callback, 'f', true };
+    handler  = { handler, 'f', true };
   }
   local client_request_ids = {}
 
@@ -1015,7 +1018,7 @@ function lsp.buf_request(bufnr, method, params, callback)
   for_each_buffer_client(bufnr, function(client, client_id, resolved_bufnr)
     if client.supports_method(method) then
       method_supported = true
-      local request_success, request_id = client.request(method, params, callback, resolved_bufnr)
+      local request_success, request_id = client.request(method, params, handler, resolved_bufnr)
 
       -- This could only fail if the client shut down in the time since we looked
       -- it up and we did the request, which should be rare.
@@ -1025,13 +1028,13 @@ function lsp.buf_request(bufnr, method, params, callback)
     end
   end)
 
-  -- if no clients support the given method, call the callback with the proper
+  -- if no clients support the given method, call the handler with the proper
   -- error message.
   if not method_supported then
     local unsupported_err = lsp._unsupported_method(method)
-    local cb = callback or lsp.callbacks[method]
-    if cb then
-      cb(unsupported_err, method, bufnr)
+    handler = handler or lsp.handlers[method]
+    if handler then
+      handler(unsupported_err, method, bufnr)
     end
     return
   end
@@ -1064,11 +1067,11 @@ end
 function lsp.buf_request_sync(bufnr, method, params, timeout_ms)
   local request_results = {}
   local result_count = 0
-  local function _callback(err, _method, result, client_id)
+  local function _sync_handler(err, _, result, client_id)
     request_results[client_id] = { error = err, result = result }
     result_count = result_count + 1
   end
-  local client_request_ids, cancel = lsp.buf_request(bufnr, method, params, _callback)
+  local client_request_ids, cancel = lsp.buf_request(bufnr, method, params, _sync_handler)
   local expected_result_count = 0
   for _ in pairs(client_request_ids) do
     expected_result_count = expected_result_count + 1
@@ -1209,22 +1212,53 @@ function lsp.get_log_path()
   return log.get_filename()
 end
 
--- Defines the LspDiagnostics signs if they're not defined already.
-do
-  --@private
-  --- Defines a sign if it isn't already defined.
-  --@param name (String) Name of the sign
-  --@param properties (table) Properties to attach to the sign
-  local function define_default_sign(name, properties)
-    if vim.tbl_isempty(vim.fn.sign_getdefined(name)) then
-      vim.fn.sign_define(name, properties)
+--- Call {fn} for every client attached to {bufnr}
+function lsp.for_each_buffer_client(bufnr, fn)
+  return for_each_buffer_client(bufnr, fn)
+end
+
+--- Function to manage overriding defaults for LSP handlers.
+--@param handler (function) See |lsp-handler|
+--@param override_config (table) Table containing the keys to override behavior of the {handler}
+function lsp.with(handler, override_config)
+  return function(err, method, params, client_id, bufnr, config)
+    return handler(err, method, params, client_id, bufnr, vim.tbl_deep_extend("force", config or {}, override_config))
+  end
+end
+
+--- Helper function to use when implementing a handler.
+--- This will check that all of the keys in the user configuration
+--- are valid keys and make sense to include for this handler.
+---
+--- Will error on invalid keys (i.e. keys that do not exist in the options)
+function lsp._with_extend(name, options, user_config)
+  user_config = user_config or {}
+
+  local resulting_config = {}
+  for k, v in pairs(user_config) do
+    if options[k] == nil then
+      error(debug.traceback(string.format(
+        "Invalid option for `%s`: %s. Valid options are:\n%s",
+        name,
+        k,
+        vim.inspect(vim.tbl_keys(options))
+      )))
     end
+
+    resulting_config[k] = v
   end
-  define_default_sign('LspDiagnosticsErrorSign', {text='E', texthl='LspDiagnosticsErrorSign', linehl='', numhl=''})
-  define_default_sign('LspDiagnosticsWarningSign', {text='W', texthl='LspDiagnosticsWarningSign', linehl='', numhl=''})
-  define_default_sign('LspDiagnosticsInformationSign', {text='I', texthl='LspDiagnosticsInformationSign', linehl='', numhl=''})
-  define_default_sign('LspDiagnosticsHintSign', {text='H', texthl='LspDiagnosticsHintSign', linehl='', numhl=''})
+
+  for k, v in pairs(options) do
+    if resulting_config[k] == nil then
+      resulting_config[k] = v
+    end
+  end
+
+  return resulting_config
 end
 
+-- Define the LspDiagnostics signs if they're not defined already.
+require('vim.lsp.diagnostic')._define_default_signs_and_highlights()
+
 return lsp
 -- vim:sw=2 ts=2 et
diff --git a/runtime/lua/vim/lsp/buf.lua b/runtime/lua/vim/lsp/buf.lua
index 0b8e08f36c..fa62905c0a 100644
--- a/runtime/lua/vim/lsp/buf.lua
+++ b/runtime/lua/vim/lsp/buf.lua
@@ -30,9 +30,7 @@ end
 ---
 --@param method (string) LSP method name
 --@param params (optional, table) Parameters to send to the server
---@param callback (optional, functionnil) Handler
---  `function(err, method, params, client_id)` for this request. Defaults
---  to the client callback in `client.callbacks`. See |lsp-callbacks|.
+--@param handler (optional, functionnil) See |lsp-handler|. Follows |lsp-handler-resolution|
 --
 --@returns 2-tuple:
 ---  - Map of client-id:request-id pairs for all successful requests.
@@ -40,12 +38,12 @@ end
 ---    iterate all clients and call their `cancel_request()` methods.
 ---
 --@see |vim.lsp.buf_request()|
-local function request(method, params, callback)
+local function request(method, params, handler)
   validate {
     method = {method, 's'};
-    callback = {callback, 'f', true};
+    handler = {handler, 'f', true};
   }
-  return vim.lsp.buf_request(0, method, params, callback)
+  return vim.lsp.buf_request(0, method, params, handler)
 end
 
 --- Checks whether the language servers attached to the current buffer are
@@ -64,6 +62,7 @@ function M.hover()
 end
 
 --- Jumps to the declaration of the symbol under the cursor.
+--@note Many servers do not implement this method. Generally, see |vim.lsp.buf.definition()| instead.
 ---
 function M.declaration()
   local params = util.make_position_params()
@@ -279,7 +278,7 @@ end
 --@see https://microsoft.github.io/language-server-protocol/specifications/specification-current/#textDocument_codeAction
 function M.code_action(context)
   validate { context = { context, 't', true } }
-  context = context or { diagnostics = util.get_line_diagnostics() }
+  context = context or { diagnostics = vim.lsp.diagnostic.get_line_diagnostics() }
   local params = util.make_range_params()
   params.context = context
   request('textDocument/codeAction', params)
@@ -294,7 +293,7 @@ end
 ---Defaults to the end of the last visual selection.
 function M.range_code_action(context, start_pos, end_pos)
   validate { context = { context, 't', true } }
-  context = context or { diagnostics = util.get_line_diagnostics() }
+  context = context or { diagnostics = vim.lsp.diagnostic.get_line_diagnostics() }
   local params = util.make_given_range_params(start_pos, end_pos)
   params.context = context
   request('textDocument/codeAction', params)
diff --git a/runtime/lua/vim/lsp/callbacks.lua b/runtime/lua/vim/lsp/callbacks.lua
index 3270d1d2a9..1da92b900d 100644
--- a/runtime/lua/vim/lsp/callbacks.lua
+++ b/runtime/lua/vim/lsp/callbacks.lua
@@ -1,345 +1,4 @@
-local log = require 'vim.lsp.log'
-local protocol = require 'vim.lsp.protocol'
 local util = require 'vim.lsp.util'
-local vim = vim
-local api = vim.api
-local buf = require 'vim.lsp.buf'
 
-local M = {}
-
--- FIXME: DOC: Expose in vimdocs
-
---@private
---- Writes to error buffer.
---@param ... (table of strings) Will be concatenated before being written
-local function err_message(...)
-  api.nvim_err_writeln(table.concat(vim.tbl_flatten{...}))
-  api.nvim_command("redraw")
-end
-
---@see https://microsoft.github.io/language-server-protocol/specifications/specification-current/#workspace_executeCommand
-M['workspace/executeCommand'] = function(err, _)
-  if err then
-    error("Could not execute code action: "..err.message)
-  end
-end
-
---@see https://microsoft.github.io/language-server-protocol/specifications/specification-current/#textDocument_codeAction
-M['textDocument/codeAction'] = function(_, _, actions)
-  if actions == nil or vim.tbl_isempty(actions) then
-    print("No code actions available")
-    return
-  end
-
-  local option_strings = {"Code Actions:"}
-  for i, action in ipairs(actions) do
-    local title = action.title:gsub('\r\n', '\\r\\n')
-    title = title:gsub('\n', '\\n')
-    table.insert(option_strings, string.format("%d. %s", i, title))
-  end
-
-  local choice = vim.fn.inputlist(option_strings)
-  if choice < 1 or choice > #actions then
-    return
-  end
-  local action_chosen = actions[choice]
-  -- textDocument/codeAction can return either Command[] or CodeAction[].
-  -- If it is a CodeAction, it can have either an edit, a command or both.
-  -- Edits should be executed first
-  if action_chosen.edit or type(action_chosen.command) == "table" then
-    if action_chosen.edit then
-      util.apply_workspace_edit(action_chosen.edit)
-    end
-    if type(action_chosen.command) == "table" then
-      buf.execute_command(action_chosen.command)
-    end
-  else
-    buf.execute_command(action_chosen)
-  end
-end
-
---@see https://microsoft.github.io/language-server-protocol/specifications/specification-current/#workspace_applyEdit
-M['workspace/applyEdit'] = function(_, _, workspace_edit)
-  if not workspace_edit then return end
-  -- TODO(ashkan) Do something more with label?
-  if workspace_edit.label then
-    print("Workspace edit", workspace_edit.label)
-  end
-  local status, result = pcall(util.apply_workspace_edit, workspace_edit.edit)
-  return {
-    applied = status;
-    failureReason = result;
-  }
-end
-
---@see https://microsoft.github.io/language-server-protocol/specifications/specification-current/#textDocument_publishDiagnostics
-M['textDocument/publishDiagnostics'] = function(_, _, result)
-  if not result then return end
-  local uri = result.uri
-  local bufnr = vim.uri_to_bufnr(uri)
-  if not bufnr then
-    err_message("LSP.publishDiagnostics: Couldn't find buffer for ", uri)
-    return
-  end
-
-  -- https://microsoft.github.io/language-server-protocol/specifications/specification-current/#diagnostic
-  -- The diagnostic's severity. Can be omitted. If omitted it is up to the
-  -- client to interpret diagnostics as error, warning, info or hint.
-  -- TODO: Replace this with server-specific heuristics to infer severity.
-  for _, diagnostic in ipairs(result.diagnostics) do
-    if diagnostic.severity == nil then
-      diagnostic.severity = protocol.DiagnosticSeverity.Error
-    end
-  end
-
-  util.buf_clear_diagnostics(bufnr)
-
-  -- Always save the diagnostics, even if the buf is not loaded.
-  -- Language servers may report compile or build errors via diagnostics
-  -- Users should be able to find these, even if they're in files which
-  -- are not loaded.
-  util.buf_diagnostics_save_positions(bufnr, result.diagnostics)
-
-  -- Unloaded buffers should not handle diagnostics.
-  --    When the buffer is loaded, we'll call on_attach, which sends textDocument/didOpen.
-  --    This should trigger another publish of the diagnostics.
-  --
-  -- In particular, this stops a ton of spam when first starting a server for current
-  -- unloaded buffers.
-  if not api.nvim_buf_is_loaded(bufnr) then
-    return
-  end
-  util.buf_diagnostics_underline(bufnr, result.diagnostics)
-  util.buf_diagnostics_virtual_text(bufnr, result.diagnostics)
-  util.buf_diagnostics_signs(bufnr, result.diagnostics)
-  vim.api.nvim_command("doautocmd User LspDiagnosticsChanged")
-end
-
---@see https://microsoft.github.io/language-server-protocol/specifications/specification-current/#textDocument_references
-M['textDocument/references'] = function(_, _, result)
-  if not result then return end
-  util.set_qflist(util.locations_to_items(result))
-  api.nvim_command("copen")
-  api.nvim_command("wincmd p")
-end
-
---@private
---- Prints given list of symbols to the quickfix list.
---@param _ (not used)
---@param _ (not used)
---@param result (list of Symbols) LSP method name
---@param result (table) result of LSP method; a location or a list of locations.
----(`textDocument/definition` can return `Location` or `Location[]`
-local symbol_callback = function(_, _, result, _, bufnr)
-  if not result or vim.tbl_isempty(result) then return end
-
-  util.set_qflist(util.symbols_to_items(result, bufnr))
-  api.nvim_command("copen")
-  api.nvim_command("wincmd p")
-end
---@see https://microsoft.github.io/language-server-protocol/specifications/specification-current/#textDocument_documentSymbol
-M['textDocument/documentSymbol'] = symbol_callback
---@see https://microsoft.github.io/language-server-protocol/specifications/specification-current/#workspace_symbol
-M['workspace/symbol'] = symbol_callback
-
---@see https://microsoft.github.io/language-server-protocol/specifications/specification-current/#textDocument_rename
-M['textDocument/rename'] = function(_, _, result)
-  if not result then return end
-  util.apply_workspace_edit(result)
-end
-
---@see https://microsoft.github.io/language-server-protocol/specifications/specification-current/#textDocument_rangeFormatting
-M['textDocument/rangeFormatting'] = function(_, _, result)
-  if not result then return end
-  util.apply_text_edits(result)
-end
-
---@see https://microsoft.github.io/language-server-protocol/specifications/specification-current/#textDocument_formatting
-M['textDocument/formatting'] = function(_, _, result)
-  if not result then return end
-  util.apply_text_edits(result)
-end
-
---@see https://microsoft.github.io/language-server-protocol/specifications/specification-current/#textDocument_completion
-M['textDocument/completion'] = function(_, _, result)
-  if vim.tbl_isempty(result or {}) then return end
-  local row, col = unpack(api.nvim_win_get_cursor(0))
-  local line = assert(api.nvim_buf_get_lines(0, row-1, row, false)[1])
-  local line_to_cursor = line:sub(col+1)
-  local textMatch = vim.fn.match(line_to_cursor, '\\k*$')
-  local prefix = line_to_cursor:sub(textMatch+1)
-
-  local matches = util.text_document_completion_list_to_complete_items(result, prefix)
-  vim.fn.complete(textMatch+1, matches)
-end
-
---@see https://microsoft.github.io/language-server-protocol/specifications/specification-current/#textDocument_hover
-M['textDocument/hover'] = function(_, method, result)
-  util.focusable_float(method, function()
-    if not (result and result.contents) then
-      -- return { 'No information available' }
-      return
-    end
-    local markdown_lines = util.convert_input_to_markdown_lines(result.contents)
-    markdown_lines = util.trim_empty_lines(markdown_lines)
-    if vim.tbl_isempty(markdown_lines) then
-      -- return { 'No information available' }
-      return
-    end
-    local bufnr, winnr = util.fancy_floating_markdown(markdown_lines, {
-      pad_left = 1; pad_right = 1;
-    })
-    util.close_preview_autocmd({"CursorMoved", "BufHidden", "InsertCharPre"}, winnr)
-    return bufnr, winnr
-  end)
-end
-
---@private
---- Jumps to a location. Used as a callback for multiple LSP methods.
---@param _ (not used)
---@param method (string) LSP method name
---@param result (table) result of LSP method; a location or a list of locations.
----(`textDocument/definition` can return `Location` or `Location[]`
-local function location_callback(_, method, result)
-  if result == nil or vim.tbl_isempty(result) then
-    local _ = log.info() and log.info(method, 'No location found')
-    return nil
-  end
-
-  -- textDocument/definition can return Location or Location[]
-  -- https://microsoft.github.io/language-server-protocol/specifications/specification-current/#textDocument_definition
-
-  if vim.tbl_islist(result) then
-    util.jump_to_location(result[1])
-
-    if #result > 1 then
-      util.set_qflist(util.locations_to_items(result))
-      api.nvim_command("copen")
-      api.nvim_command("wincmd p")
-    end
-  else
-    util.jump_to_location(result)
-  end
-end
-
---@see https://microsoft.github.io/language-server-protocol/specifications/specification-current/#textDocument_declaration
-M['textDocument/declaration'] = location_callback
---@see https://microsoft.github.io/language-server-protocol/specifications/specification-current/#textDocument_definition
-M['textDocument/definition'] = location_callback
---@see https://microsoft.github.io/language-server-protocol/specifications/specification-current/#textDocument_typeDefinition
-M['textDocument/typeDefinition'] = location_callback
---@see https://microsoft.github.io/language-server-protocol/specifications/specification-current/#textDocument_implementation
-M['textDocument/implementation'] = location_callback
-
---@see https://microsoft.github.io/language-server-protocol/specifications/specification-current/#textDocument_signatureHelp
-M['textDocument/signatureHelp'] = function(_, method, result)
-  -- When use `autocmd CompleteDone <silent><buffer> lua vim.lsp.buf.signature_help()` to call signatureHelp callback
-  -- If the completion item doesn't have signatures It will make noise. Change to use `print` that can use `<silent>` to ignore
-  if not (result and result.signatures and result.signatures[1]) then
-    print('No signature help available')
-    return
-  end
-  local lines = util.convert_signature_help_to_markdown_lines(result)
-  lines = util.trim_empty_lines(lines)
-  if vim.tbl_isempty(lines) then
-    print('No signature help available')
-    return
-  end
-  util.focusable_preview(method, function()
-    return lines, util.try_trim_markdown_code_blocks(lines)
-  end)
-end
-
---@see https://microsoft.github.io/language-server-protocol/specifications/specification-current/#textDocument_documentHighlight
-M['textDocument/documentHighlight'] = function(_, _, result, _)
-  if not result then return end
-  local bufnr = api.nvim_get_current_buf()
-  util.buf_highlight_references(bufnr, result)
-end
-
---@private
----
---- Displays call hierarchy in the quickfix window.
----
---@param direction `"from"` for incoming calls and `"to"` for outgoing calls
---@returns `CallHierarchyIncomingCall[]` if {direction} is `"from"`,
---@returns `CallHierarchyOutgoingCall[]` if {direction} is `"to"`,
-local make_call_hierarchy_callback = function(direction)
-  return function(_, _, result)
-    if not result then return end
-    local items = {}
-    for _, call_hierarchy_call in pairs(result) do
-      local call_hierarchy_item = call_hierarchy_call[direction]
-      for _, range in pairs(call_hierarchy_call.fromRanges) do
-        table.insert(items, {
-          filename = assert(vim.uri_to_fname(call_hierarchy_item.uri)),
-          text = call_hierarchy_item.name,
-          lnum = range.start.line + 1,
-          col = range.start.character + 1,
-        })
-      end
-    end
-    util.set_qflist(items)
-    api.nvim_command("copen")
-    api.nvim_command("wincmd p")
-  end
-end
-
---@see https://microsoft.github.io/language-server-protocol/specifications/specification-current/#callHierarchy/incomingCalls
-M['callHierarchy/incomingCalls'] = make_call_hierarchy_callback('from')
-
---@see https://microsoft.github.io/language-server-protocol/specifications/specification-current/#callHierarchy/outgoingCalls
-M['callHierarchy/outgoingCalls'] = make_call_hierarchy_callback('to')
-
---@see https://microsoft.github.io/language-server-protocol/specifications/specification-current/#window/logMessage
-M['window/logMessage'] = function(_, _, result, client_id)
-  local message_type = result.type
-  local message = result.message
-  local client = vim.lsp.get_client_by_id(client_id)
-  local client_name = client and client.name or string.format("id=%d", client_id)
-  if not client then
-    err_message("LSP[", client_name, "] client has shut down after sending the message")
-  end
-  if message_type == protocol.MessageType.Error then
-    log.error(message)
-  elseif message_type == protocol.MessageType.Warning then
-    log.warn(message)
-  elseif message_type == protocol.MessageType.Info then
-    log.info(message)
-  else
-    log.debug(message)
-  end
-  return result
-end
-
---@see https://microsoft.github.io/language-server-protocol/specifications/specification-current/#window/showMessage
-M['window/showMessage'] = function(_, _, result, client_id)
-  local message_type = result.type
-  local message = result.message
-  local client = vim.lsp.get_client_by_id(client_id)
-  local client_name = client and client.name or string.format("id=%d", client_id)
-  if not client then
-    err_message("LSP[", client_name, "] client has shut down after sending the message")
-  end
-  if message_type == protocol.MessageType.Error then
-    err_message("LSP[", client_name, "] ", message)
-  else
-    local message_type_name = protocol.MessageType[message_type]
-    api.nvim_out_write(string.format("LSP[%s][%s] %s\n", client_name, message_type_name, message))
-  end
-  return result
-end
-
--- Add boilerplate error validation and logging for all of these.
-for k, fn in pairs(M) do
-  M[k] = function(err, method, params, client_id, bufnr)
-    log.debug('default_callback', method, { params = params, client_id = client_id, err = err, bufnr = bufnr })
-    if err then
-      error(tostring(err))
-    end
-    return fn(err, method, params, client_id, bufnr)
-  end
-end
-
-return M
--- vim:sw=2 ts=2 et
+util._warn_once("require('vim.lsp.callbacks') is deprecated. Use vim.lsp.handlers instead.")
+return require('vim.lsp.handlers')
diff --git a/runtime/lua/vim/lsp/diagnostic.lua b/runtime/lua/vim/lsp/diagnostic.lua
new file mode 100644
index 0000000000..590d694826
--- /dev/null
+++ b/runtime/lua/vim/lsp/diagnostic.lua
@@ -0,0 +1,1195 @@
+local api = vim.api
+local validate = vim.validate
+
+local highlight = vim.highlight
+local log = require('vim.lsp.log')
+local protocol = require('vim.lsp.protocol')
+local util = require('vim.lsp.util')
+
+local if_nil = vim.F.if_nil
+
+--@class DiagnosticSeverity
+local DiagnosticSeverity = protocol.DiagnosticSeverity
+
+local to_severity = function(severity)
+  if not severity then return nil end
+  return type(severity) == 'string' and DiagnosticSeverity[severity] or severity
+end
+
+local to_position = function(position, bufnr)
+  vim.validate { position = {position, 't'} }
+
+  return {
+    position.line,
+    util._get_line_byte_from_position(bufnr, position)
+  }
+end
+
+
+---@brief lsp-diagnostic
+---
+--@class Diagnostic
+--@field range Range
+--@field message string
+--@field severity DiagnosticSeverity|nil
+--@field code number | string
+--@field source string
+--@field tags DiagnosticTag[]
+--@field relatedInformation DiagnosticRelatedInformation[]
+
+local M = {}
+
+-- Diagnostic Highlights {{{
+
+-- TODO(tjdevries): Determine how to generate documentation for these
+--                  and how to configure them to be easy for users.
+--
+--                  For now, just use the following script. It should work pretty good.
+--[[
+local levels = {"Error", "Warning", "Information", "Hint" }
+
+local all_info = {
+  { "Default", "Used as the base highlight group, other highlight groups link to", },
+  { "VirtualText", 'Used for "%s" diagnostic virtual text.\n  See |vim.lsp.diagnostic.set_virtual_text()|', },
+  { "Underline", 'Used to underline "%s" diagnostics.\n  See |vim.lsp.diagnostic.set_underline()|', },
+  { "Floating", 'Used to color "%s" diagnostic messages in diagnostics float.\n  See |vim.lsp.diagnostic.show_line_diagnostics()|', },
+  { "Sign", 'Used for "%s" signs in sing column.\n  See |vim.lsp.diagnostic.set_signs()|', },
+}
+
+local results = {}
+for _, info in ipairs(all_info) do
+  for _, level in ipairs(levels) do
+    local name = info[1]
+    local description = info[2]
+    local fullname = string.format("Lsp%s%s", name, level)
+    table.insert(results, string.format(
+      "%78s", string.format("*hl-%s*", fullname))
+    )
+
+    table.insert(results, fullname)
+    table.insert(results, string.format("  %s", description))
+    table.insert(results, "")
+  end
+end
+
+-- print(table.concat(results, '\n'))
+vim.fn.setreg("*", table.concat(results, '\n'))
+--]]
+
+local diagnostic_severities = {
+  [DiagnosticSeverity.Error]       = { guifg = "Red" };
+  [DiagnosticSeverity.Warning]     = { guifg = "Orange" };
+  [DiagnosticSeverity.Information] = { guifg = "LightBlue" };
+  [DiagnosticSeverity.Hint]        = { guifg = "LightGrey" };
+}
+
+-- Make a map from DiagnosticSeverity -> Highlight Name
+local make_highlight_map = function(base_name)
+  local result = {}
+  for k, _ in pairs(diagnostic_severities) do
+    result[k] = "LspDiagnostics" .. base_name .. DiagnosticSeverity[k]
+  end
+
+  return result
+end
+
+local default_highlight_map = make_highlight_map("Default")
+local virtual_text_highlight_map = make_highlight_map("VirtualText")
+local underline_highlight_map = make_highlight_map("Underline")
+local floating_highlight_map = make_highlight_map("Floating")
+local sign_highlight_map = make_highlight_map("Sign")
+
+-- }}}
+-- Diagnostic Namespaces {{{
+local DEFAULT_CLIENT_ID = -1
+local get_client_id = function(client_id)
+  if client_id == nil then
+    client_id = DEFAULT_CLIENT_ID
+  end
+
+  return client_id
+end
+
+local get_bufnr = function(bufnr)
+  if not bufnr then
+    return api.nvim_get_current_buf()
+  elseif bufnr == 0 then
+    return api.nvim_get_current_buf()
+  end
+
+  return bufnr
+end
+
+
+--- Create a namespace table, used to track a client's buffer local items
+local _make_namespace_table = function(namespace, api_namespace)
+  vim.validate { namespace = { namespace, 's' } }
+
+  return setmetatable({
+    [DEFAULT_CLIENT_ID] = api.nvim_create_namespace(namespace)
+  }, {
+    __index = function(t, client_id)
+      client_id = get_client_id(client_id)
+
+      if rawget(t, client_id) == nil then
+        local value = string.format("%s:%s", namespace, client_id)
+
+        if api_namespace then
+          value = api.nvim_create_namespace(value)
+        end
+
+        rawset(t, client_id, value)
+      end
+
+      return rawget(t, client_id)
+    end
+  })
+end
+
+local _diagnostic_namespaces = _make_namespace_table("vim_lsp_diagnostics", true)
+local _sign_namespaces = _make_namespace_table("vim_lsp_signs", false)
+
+--@private
+function M._get_diagnostic_namespace(client_id)
+  return _diagnostic_namespaces[client_id]
+end
+
+--@private
+function M._get_sign_namespace(client_id)
+  return _sign_namespaces[client_id]
+end
+-- }}}
+-- Diagnostic Buffer & Client metatables {{{
+local bufnr_and_client_cacher_mt = {
+  __index = function(t, bufnr)
+    if bufnr == 0 or bufnr == nil then
+      bufnr = vim.api.nvim_get_current_buf()
+    end
+
+    if rawget(t, bufnr) == nil then
+      rawset(t, bufnr, {})
+    end
+
+    return rawget(t, bufnr)
+  end,
+
+  __newindex = function(t, bufnr, v)
+    if bufnr == 0 or bufnr == nil then
+      bufnr = vim.api.nvim_get_current_buf()
+    end
+
+    rawset(t, bufnr, v)
+  end,
+}
+-- }}}
+-- Diagnostic Saving & Caching {{{
+local _diagnostic_cleanup = setmetatable({}, bufnr_and_client_cacher_mt)
+local diagnostic_cache = setmetatable({}, bufnr_and_client_cacher_mt)
+local diagnostic_cache_lines = setmetatable({}, bufnr_and_client_cacher_mt)
+local diagnostic_cache_counts = setmetatable({}, bufnr_and_client_cacher_mt)
+
+local _bufs_waiting_to_update = setmetatable({}, bufnr_and_client_cacher_mt)
+
+--- Store Diagnostic[] by line
+---
+---@param diagnostics Diagnostic[]
+---@return table<number, Diagnostic[]>
+local _diagnostic_lines = function(diagnostics)
+  if not diagnostics then return end
+
+  local diagnostics_by_line = {}
+  for _, diagnostic in ipairs(diagnostics) do
+    local start = diagnostic.range.start
+    local line_diagnostics = diagnostics_by_line[start.line]
+    if not line_diagnostics then
+      line_diagnostics = {}
+      diagnostics_by_line[start.line] = line_diagnostics
+    end
+    table.insert(line_diagnostics, diagnostic)
+  end
+  return diagnostics_by_line
+end
+
+--- Get the count of M by Severity
+---
+---@param diagnostics Diagnostic[]
+---@return table<DiagnosticSeverity, number>
+local _diagnostic_counts = function(diagnostics)
+  if not diagnostics then return end
+
+  local counts = {}
+  for _, diagnostic in pairs(diagnostics) do
+    if diagnostic.severity then
+      local val = counts[diagnostic.severity]
+      if val == nil then
+        val = 0
+      end
+
+      counts[diagnostic.severity] = val + 1
+    end
+  end
+
+  return counts
+end
+
+--@private
+--- Set the different diagnostic cache after `textDocument/publishDiagnostics`
+---@param diagnostics Diagnostic[]
+---@param bufnr number
+---@param client_id number
+---@return nil
+local function set_diagnostic_cache(diagnostics, bufnr, client_id)
+  client_id = get_client_id(client_id)
+
+  -- https://microsoft.github.io/language-server-protocol/specifications/specification-current/#diagnostic
+  --
+  -- The diagnostic's severity. Can be omitted. If omitted it is up to the
+  -- client to interpret diagnostics as error, warning, info or hint.
+  -- TODO: Replace this with server-specific heuristics to infer severity.
+  for _, diagnostic in ipairs(diagnostics) do
+    if diagnostic.severity == nil then
+      diagnostic.severity = DiagnosticSeverity.Error
+    end
+  end
+
+  diagnostic_cache[bufnr][client_id] = diagnostics
+  diagnostic_cache_lines[bufnr][client_id] = _diagnostic_lines(diagnostics)
+  diagnostic_cache_counts[bufnr][client_id] = _diagnostic_counts(diagnostics)
+end
+
+
+--@private
+--- Clear the cached diagnostics
+---@param bufnr number
+---@param client_id number
+local function clear_diagnostic_cache(bufnr, client_id)
+  client_id = get_client_id(client_id)
+
+  diagnostic_cache[bufnr][client_id] = nil
+  diagnostic_cache_lines[bufnr][client_id] = nil
+  diagnostic_cache_counts[bufnr][client_id] = nil
+end
+
+--- Save diagnostics to the current buffer.
+---
+--- Handles saving diagnostics from multiple clients in the same buffer.
+---@param diagnostics Diagnostic[]
+---@param bufnr number
+---@param client_id number
+function M.save(diagnostics, bufnr, client_id)
+  validate {
+    diagnostics = {diagnostics, 't'},
+    bufnr = {bufnr, 'n'},
+    client_id = {client_id, 'n', true},
+  }
+
+  if not diagnostics then return end
+
+  bufnr = get_bufnr(bufnr)
+  client_id = get_client_id(client_id)
+
+  if not _diagnostic_cleanup[bufnr][client_id] then
+    _diagnostic_cleanup[bufnr][client_id] = true
+
+    -- Clean up our data when the buffer unloads.
+    api.nvim_buf_attach(bufnr, false, {
+      on_detach = function(b)
+        clear_diagnostic_cache(b, client_id)
+        _diagnostic_cleanup[bufnr][client_id] = nil
+      end
+    })
+  end
+
+  set_diagnostic_cache(diagnostics, bufnr, client_id)
+end
+-- }}}
+-- Diagnostic Retrieval {{{
+
+--- Return associated diagnostics for bufnr
+---
+---@param bufnr number
+---@param client_id number|nil If nil, then return all of the diagnostics.
+---                            Else, return just the diagnostics associated with the client_id.
+function M.get(bufnr, client_id)
+  if client_id == nil then
+    local all_diagnostics = {}
+    for iter_client_id, _ in pairs(diagnostic_cache[bufnr]) do
+      local iter_diagnostics = M.get(bufnr, iter_client_id)
+
+      for _, diagnostic in ipairs(iter_diagnostics) do
+        table.insert(all_diagnostics, diagnostic)
+      end
+    end
+
+    return all_diagnostics
+  end
+
+  return diagnostic_cache[bufnr][client_id] or {}
+end
+
+--- Get the diagnostics by line
+---
+---@param bufnr number The buffer number
+---@param line_nr number The line number
+---@param opts table|nil Configuration keys
+---         - severity: (DiagnosticSeverity, default nil)
+---             - Only return diagnostics with this severity. Overrides severity_limit
+---         - severity_limit: (DiagnosticSeverity, default nil)
+---             - Limit severity of diagnostics found. E.g. "Warning" means { "Error", "Warning" } will be valid.
+---@param client_id number the client id
+---@return table Table with map of line number to list of diagnostics.
+--               Structured: { [1] = {...}, [5] = {.... } }
+function M.get_line_diagnostics(bufnr, line_nr, opts, client_id)
+  opts = opts or {}
+
+  bufnr = bufnr or vim.api.nvim_get_current_buf()
+  line_nr = line_nr or vim.api.nvim_win_get_cursor(0)[1] - 1
+
+  local client_get_diags = function(iter_client_id)
+    return (diagnostic_cache_lines[bufnr][iter_client_id] or {})[line_nr] or {}
+  end
+
+  local line_diagnostics
+  if client_id == nil then
+    line_diagnostics = {}
+    for iter_client_id, _ in pairs(diagnostic_cache_lines[bufnr]) do
+      for _, diagnostic in ipairs(client_get_diags(iter_client_id)) do
+        table.insert(line_diagnostics, diagnostic)
+      end
+    end
+  else
+    line_diagnostics = vim.deepcopy(client_get_diags(client_id))
+  end
+
+  if opts.severity then
+    local filter_level = to_severity(opts.severity)
+    line_diagnostics = vim.tbl_filter(function(t) return t.severity == filter_level end, line_diagnostics)
+  elseif opts.severity_limit then
+    local filter_level = to_severity(opts.severity_limit)
+    line_diagnostics = vim.tbl_filter(function(t) return t.severity <= filter_level end, line_diagnostics)
+  end
+
+  if opts.severity_sort then
+    table.sort(line_diagnostics, function(a, b) return a.severity < b.severity end)
+  end
+
+  return line_diagnostics
+end
+
+--- Get the counts for a particular severity
+---
+--- Useful for showing diagnostic counts in statusline. eg:
+---
+--- <pre>
+--- function! LspStatus() abort
+---   let sl = ''
+---   if luaeval('not vim.tbl_isempty(vim.lsp.buf_get_clients(0))')
+---     let sl.='%#MyStatuslineLSP#E:'
+---     let sl.='%#MyStatuslineLSPErrors#%{luaeval("vim.lsp.diagnostic.get_count([[Error]])")}'
+---     let sl.='%#MyStatuslineLSP# W:'
+---     let sl.='%#MyStatuslineLSPWarnings#%{luaeval("vim.lsp.diagnostic.get_count([[Warning]])")}'
+---   else
+---       let sl.='%#MyStatuslineLSPErrors#off'
+---   endif
+---   return sl
+--- endfunction
+--- let &l:statusline = '%#MyStatuslineLSP#LSP '.LspStatus()
+--- </pre>
+---
+---@param bufnr number The buffer number
+---@param severity DiagnosticSeverity
+---@param client_id number the client id
+function M.get_count(bufnr, severity, client_id)
+  if client_id == nil then
+    local total = 0
+    for iter_client_id, _ in pairs(diagnostic_cache_counts[bufnr]) do
+      total = total + M.get_count(bufnr, severity, iter_client_id)
+    end
+
+    return total
+  end
+
+  return (diagnostic_cache_counts[bufnr][client_id] or {})[DiagnosticSeverity[severity]] or 0
+end
+
+
+-- }}}
+-- Diagnostic Movements {{{
+
+--- Helper function to iterate through all of the diagnostic lines
+---@return table list of diagnostics
+local _iter_diagnostic_lines = function(start, finish, step, bufnr, opts, client_id)
+  if bufnr == nil then
+    bufnr = vim.api.nvim_get_current_buf()
+  end
+
+  local wrap = if_nil(opts.wrap, true)
+
+  local search = function(search_start, search_finish, search_step)
+    for line_nr = search_start, search_finish, search_step do
+      local line_diagnostics = M.get_line_diagnostics(bufnr, line_nr, opts, client_id)
+      if line_diagnostics and not vim.tbl_isempty(line_diagnostics) then
+        return line_diagnostics
+      end
+    end
+  end
+
+  local result = search(start, finish, step)
+
+  if wrap then
+    local wrap_start, wrap_finish
+    if step == 1 then
+      wrap_start, wrap_finish = 1, start
+    else
+      wrap_start, wrap_finish = vim.api.nvim_buf_line_count(bufnr), start
+    end
+
+    if not result then
+      result = search(wrap_start, wrap_finish, step)
+    end
+  end
+
+  return result
+end
+
+--@private
+--- Helper function to ierate through diagnostic lines and return a position
+---
+---@return table {row, col}
+local function _iter_diagnostic_lines_pos(opts, line_diagnostics)
+  opts = opts or {}
+
+  local win_id = opts.win_id or vim.api.nvim_get_current_win()
+  local bufnr = vim.api.nvim_win_get_buf(win_id)
+
+  if line_diagnostics == nil or vim.tbl_isempty(line_diagnostics) then
+    return false
+  end
+
+  local iter_diagnostic = line_diagnostics[1]
+  return to_position(iter_diagnostic.range.start, bufnr)
+end
+
+--@private
+-- Move to the diagnostic position
+local function _iter_diagnostic_move_pos(name, opts, pos)
+  opts = opts or {}
+
+  local enable_popup = if_nil(opts.enable_popup, true)
+  local win_id = opts.win_id or vim.api.nvim_get_current_win()
+
+  if not pos then
+    print(string.format("%s: No more valid diagnostics to move to.", name))
+    return
+  end
+
+  vim.api.nvim_win_set_cursor(win_id, {pos[1] + 1, pos[2]})
+
+  if enable_popup then
+    -- This is a bit weird... I'm surprised that we need to wait til the next tick to do this.
+    vim.schedule(function()
+      M.show_line_diagnostics(opts.popup_opts, vim.api.nvim_win_get_buf(win_id))
+    end)
+  end
+end
+
+--- Get the previous diagnostic closest to the cursor_position
+---
+---@param opts table See |vim.lsp.diagnostics.goto_next()|
+---@return table Previous diagnostic
+function M.get_prev(opts)
+  opts = opts or {}
+
+  local win_id = opts.win_id or vim.api.nvim_get_current_win()
+  local bufnr = vim.api.nvim_win_get_buf(win_id)
+  local cursor_position = opts.cursor_position or vim.api.nvim_win_get_cursor(win_id)
+
+  return _iter_diagnostic_lines(cursor_position[1] - 2, 0, -1, bufnr, opts, opts.client_id)
+end
+
+--- Return the pos, {row, col}, for the prev diagnostic in the current buffer.
+---@param opts table See |vim.lsp.diagnostics.goto_next()|
+---@return table Previous diagnostic position
+function M.get_prev_pos(opts)
+  return _iter_diagnostic_lines_pos(
+    opts,
+    M.get_prev(opts)
+  )
+end
+
+--- Move to the previous diagnostic
+---@param opts table See |vim.lsp.diagnostics.goto_next()|
+function M.goto_prev(opts)
+  return _iter_diagnostic_move_pos(
+    "DiagnosticPrevious",
+    opts,
+    M.get_prev_pos(opts)
+  )
+end
+
+--- Get the previous diagnostic closest to the cursor_position
+---@param opts table See |vim.lsp.diagnostics.goto_next()|
+---@return table Next diagnostic
+function M.get_next(opts)
+  opts = opts or {}
+
+  local win_id = opts.win_id or vim.api.nvim_get_current_win()
+  local bufnr = vim.api.nvim_win_get_buf(win_id)
+  local cursor_position = opts.cursor_position or vim.api.nvim_win_get_cursor(win_id)
+
+  return _iter_diagnostic_lines(cursor_position[1], vim.api.nvim_buf_line_count(bufnr), 1, bufnr, opts, opts.client_id)
+end
+
+--- Return the pos, {row, col}, for the next diagnostic in the current buffer.
+---@param opts table See |vim.lsp.diagnostics.goto_next()|
+---@return table Next diagnostic position
+function M.get_next_pos(opts)
+  return _iter_diagnostic_lines_pos(
+    opts,
+    M.get_next(opts)
+  )
+end
+
+--- Move to the next diagnostic
+---@param opts table|nil Configuration table. Keys:
+---         - {client_id}: (number)
+---             - If nil, will consider all clients attached to buffer.
+---         - {cursor_position}: (Position, default current position)
+---             - See |nvim_win_get_cursor()|
+---         - {wrap}: (boolean, default true)
+---             - Whether to loop around file or not. Similar to 'wrapscan'
+---         - {severity}: (DiagnosticSeverity)
+---             - Exclusive severity to consider. Overrides {severity_limit}
+---         - {severity_limit}: (DiagnosticSeverity)
+---             - Limit severity of diagnostics found. E.g. "Warning" means { "Error", "Warning" } will be valid.
+---         - {enable_popup}: (boolean, default true)
+---             - Call |vim.lsp.diagnostic.show_line_diagnostics()| on jump
+---         - {popup_opts}: (table)
+---             - Table to pass as {opts} parameter to |vim.lsp.diagnostic.show_line_diagnostics()|
+---         - {win_id}: (number, default 0)
+---             - Window ID
+function M.goto_next(opts)
+  return _iter_diagnostic_move_pos(
+    "DiagnosticNext",
+    opts,
+    M.get_next_pos(opts)
+  )
+end
+-- }}}
+-- Diagnostic Setters {{{
+
+--- Set signs for given diagnostics
+---
+--- Sign characters can be customized with the following commands:
+---
+--- <pre>
+--- sign define LspDiagnosticsErrorSign text=E texthl=LspDiagnosticsError linehl= numhl=
+--- sign define LspDiagnosticsWarningSign text=W texthl=LspDiagnosticsWarning linehl= numhl=
+--- sign define LspDiagnosticsInformationSign text=I texthl=LspDiagnosticsInformation linehl= numhl=
+--- sign define LspDiagnosticsHintSign text=H texthl=LspDiagnosticsHint linehl= numhl=
+--- </pre>
+---@param diagnostics Diagnostic[]
+---@param bufnr number The buffer number
+---@param client_id number the client id
+---@param sign_ns number|nil
+---@param opts table Configuration for signs. Keys:
+---             - priority: Set the priority of the signs.
+function M.set_signs(diagnostics, bufnr, client_id, sign_ns, opts)
+  opts = opts or {}
+  sign_ns = sign_ns or M._get_sign_namespace(client_id)
+
+  if not diagnostics then
+    diagnostics = diagnostic_cache[bufnr][client_id]
+  end
+
+  if not diagnostics then
+    return
+  end
+
+  bufnr = get_bufnr(bufnr)
+
+  local ok = true
+  for _, diagnostic in ipairs(diagnostics) do
+    ok = ok and pcall(vim.fn.sign_place,
+      0,
+      sign_ns,
+      sign_highlight_map[diagnostic.severity],
+      bufnr,
+      {
+        priority = opts.priority,
+        lnum = diagnostic.range.start.line + 1
+      }
+    )
+  end
+
+  if not ok then
+    log.debug("Failed to place signs:", diagnostics)
+  end
+end
+
+--- Set underline for given diagnostics
+---
+--- Underline highlights can be customized by changing the following |:highlight| groups.
+---
+--- <pre>
+--- LspDiagnosticsUnderlineError
+--- LspDiagnosticsUnderlineWarning
+--- LspDiagnosticsUnderlineInformation
+--- LspDiagnosticsUnderlineHint
+--- </pre>
+---
+---@param diagnostics Diagnostic[]
+---@param bufnr number The buffer number
+---@param client_id number the client id
+---@param diagnostic_ns number|nil
+---@param opts table Currently unused.
+function M.set_underline(diagnostics, bufnr, client_id, diagnostic_ns, opts)
+  opts = opts or {}
+  assert(opts) -- lint
+
+  diagnostic_ns = diagnostic_ns or M._get_diagnostic_namespace(client_id)
+
+  for _, diagnostic in ipairs(diagnostics) do
+    local start = diagnostic.range["start"]
+    local finish = diagnostic.range["end"]
+    local higroup = underline_highlight_map[diagnostic.severity]
+
+    if higroup == nil then
+      -- Default to error if we don't have a highlight associated
+      higroup = underline_highlight_map[DiagnosticSeverity.Error]
+    end
+
+    highlight.range(
+      bufnr,
+      diagnostic_ns,
+      higroup,
+      to_position(start, bufnr),
+      to_position(finish, bufnr)
+    )
+  end
+end
+
+-- Virtual Text {{{
+--- Set virtual text given diagnostics
+---
+--- Virtual text highlights can be customized by changing the following |:highlight| groups.
+---
+--- <pre>
+--- LspDiagnosticsVirtualTextError
+--- LspDiagnosticsVirtualTextWarning
+--- LspDiagnosticsVirtualTextInformation
+--- LspDiagnosticsVirtualTextHint
+--- </pre>
+---
+---@param diagnostics Diagnostic[]
+---@param bufnr number
+---@param client_id number
+---@param diagnostic_ns number
+---@param opts table Options on how to display virtual text. Keys:
+---             - prefix (string): Prefix to display before virtual text on line
+---             - spacing (number): Number of spaces to insert before virtual text
+function M.set_virtual_text(diagnostics, bufnr, client_id, diagnostic_ns, opts)
+  opts = opts or {}
+
+  client_id = get_client_id(client_id)
+  diagnostic_ns = diagnostic_ns or M._get_diagnostic_namespace(client_id)
+
+  local buffer_line_diagnostics
+  if diagnostics then
+    buffer_line_diagnostics = _diagnostic_lines(diagnostics)
+  else
+    buffer_line_diagnostics = diagnostic_cache_lines[bufnr][client_id]
+  end
+
+  if not buffer_line_diagnostics then
+    return nil
+  end
+
+  for line, line_diagnostics in pairs(buffer_line_diagnostics) do
+    local virt_texts = M.get_virtual_text_chunks_for_line(bufnr, line, line_diagnostics, opts)
+
+    if virt_texts then
+      api.nvim_buf_set_virtual_text(bufnr, diagnostic_ns, line, virt_texts, {})
+    end
+  end
+end
+
+--- Default function to get text chunks to display using `nvim_buf_set_virtual_text`.
+---@param bufnr number The buffer to display the virtual text in
+---@param line number The line number to display the virtual text on
+---@param line_diags Diagnostic[] The diagnostics associated with the line
+---@param opts table See {opts} from |vim.lsp.diagnostic.set_virtual_text()|
+---@return table chunks, as defined by |nvim_buf_set_virtual_text()|
+function M.get_virtual_text_chunks_for_line(bufnr, line, line_diags, opts)
+  assert(bufnr or line)
+
+  if #line_diags == 0 then
+    return nil
+  end
+
+  opts = opts or {}
+  local prefix = opts.prefix or "■"
+  local spacing = opts.spacing or 4
+
+  -- Create a little more space between virtual text and contents
+  local virt_texts = {{string.rep(" ", spacing)}}
+
+  for i = 1, #line_diags - 1 do
+    table.insert(virt_texts, {prefix, virtual_text_highlight_map[line_diags[i].severity]})
+  end
+  local last = line_diags[#line_diags]
+
+  -- TODO(tjdevries): Allow different servers to be shown first somehow?
+  -- TODO(tjdevries): Display server name associated with these?
+  if last.message then
+    table.insert(
+      virt_texts,
+      {
+        string.format("%s %s", prefix, last.message:gsub("\r", ""):gsub("\n", "  ")),
+        virtual_text_highlight_map[last.severity]
+      }
+    )
+
+    return virt_texts
+  end
+end
+-- }}}
+-- }}}
+-- Diagnostic Clear {{{
+--- Clears the currently displayed diagnostics
+---@param bufnr number The buffer number
+---@param client_id number the client id
+---@param diagnostic_ns number|nil Associated diagnostic namespace
+---@param sign_ns number|nil Associated sign namespace
+function M.clear(bufnr, client_id, diagnostic_ns, sign_ns)
+  validate { bufnr = { bufnr, 'n' } }
+
+  bufnr = (bufnr == 0 and api.nvim_get_current_buf()) or bufnr
+
+  if client_id == nil then
+    return vim.lsp.for_each_buffer_client(bufnr, function(_, iter_client_id, _)
+      return M.clear(bufnr, iter_client_id)
+    end)
+  end
+
+  diagnostic_ns = diagnostic_ns or M._get_diagnostic_namespace(client_id)
+  sign_ns = sign_ns or M._get_sign_namespace(client_id)
+
+  assert(bufnr, "bufnr is required")
+  assert(diagnostic_ns, "Need diagnostic_ns, got nil")
+  assert(sign_ns, string.format("Need sign_ns, got nil %s", sign_ns))
+
+  -- clear sign group
+  vim.fn.sign_unplace(sign_ns, {buffer=bufnr})
+
+  -- clear virtual text namespace
+  api.nvim_buf_clear_namespace(bufnr, diagnostic_ns, 0, -1)
+end
+-- }}}
+-- Diagnostic Insert Leave Handler {{{
+
+--- Callback scheduled for after leaving insert mode
+---
+--- Used to handle
+--@private
+function M._execute_scheduled_display(bufnr, client_id)
+  local args = _bufs_waiting_to_update[bufnr][client_id]
+  if not args then
+    return
+  end
+
+  -- Clear the args so we don't display unnecessarily.
+  _bufs_waiting_to_update[bufnr][client_id] = nil
+
+  M.display(nil, bufnr, client_id, args)
+end
+
+local registered = {}
+
+local make_augroup_key = function(bufnr, client_id)
+  return string.format("LspDiagnosticInsertLeave:%s:%s", bufnr, client_id)
+end
+
+--- Table of autocmd events to fire the update for displaying new diagnostic information
+M.insert_leave_auto_cmds = { "InsertLeave", "CursorHoldI" }
+
+--- Used to schedule diagnostic updates upon leaving insert mode.
+---
+--- For parameter description, see |M.display()|
+function M._schedule_display(bufnr, client_id, args)
+  _bufs_waiting_to_update[bufnr][client_id] = args
+
+  local key = make_augroup_key(bufnr, client_id)
+  if not registered[key] then
+    vim.cmd(string.format("augroup %s", key))
+    vim.cmd("  au!")
+    vim.cmd(
+      string.format(
+        [[autocmd %s <buffer=%s> :lua vim.lsp.diagnostic._execute_scheduled_display(%s, %s)]],
+        table.concat(M.insert_leave_auto_cmds, ","),
+        bufnr,
+        bufnr,
+        client_id
+      )
+    )
+    vim.cmd("augroup END")
+
+    registered[key] = true
+  end
+end
+
+
+--- Used in tandem with
+---
+--- For parameter description, see |M.display()|
+function M._clear_scheduled_display(bufnr, client_id)
+  local key = make_augroup_key(bufnr, client_id)
+
+  if registered[key] then
+    vim.cmd(string.format("augroup %s", key))
+    vim.cmd("  au!")
+    vim.cmd("augroup END")
+
+    registered[key] = nil
+  end
+end
+-- }}}
+
+-- Diagnostic Private Highlight Utilies {{{
+--- Get the severity highlight name
+--@private
+function M._get_severity_highlight_name(severity)
+  return virtual_text_highlight_map[severity]
+end
+
+--- Get floating severity highlight name
+--@private
+function M._get_floating_severity_highlight_name(severity)
+  return floating_highlight_map[severity]
+end
+
+--- This should be called to update the highlights for the LSP client.
+function M._define_default_signs_and_highlights()
+  --@private
+  local function define_default_sign(name, properties)
+    if vim.tbl_isempty(vim.fn.sign_getdefined(name)) then
+      vim.fn.sign_define(name, properties)
+    end
+  end
+
+  -- Initialize default diagnostic highlights
+  for severity, hi_info in pairs(diagnostic_severities) do
+    local default_highlight_name = default_highlight_map[severity]
+    highlight.create(default_highlight_name, hi_info, true)
+
+    -- Default link all corresponding highlights to the default highlight
+    highlight.link(virtual_text_highlight_map[severity], default_highlight_name, false)
+    highlight.link(floating_highlight_map[severity], default_highlight_name, false)
+    highlight.link(sign_highlight_map[severity], default_highlight_name, false)
+  end
+
+  -- Create all signs
+  for severity, sign_hl_name in pairs(sign_highlight_map) do
+    local severity_name = DiagnosticSeverity[severity]
+
+    define_default_sign(sign_hl_name, {
+      text = (severity_name or 'U'):sub(1, 1),
+      texthl = sign_hl_name,
+      linehl = '',
+      numhl = '',
+    })
+  end
+
+  -- Initialize Underline highlights
+  for severity, underline_highlight_name in pairs(underline_highlight_map) do
+    highlight.create(underline_highlight_name, {
+      cterm = 'underline',
+      gui   = 'underline',
+      guisp = diagnostic_severities[severity].guifg
+    }, true)
+  end
+end
+-- }}}
+-- Diagnostic Display {{{
+
+--- |lsp-handler| for the method "textDocument/publishDiagnostics"
+---
+---@note Each of the configuration options accepts:
+---         - `false`: Disable this feature
+---         - `true`: Enable this feature, use default settings.
+---         - `table`: Enable this feature, use overrides.
+---         - `function`: Function with signature (bufnr, client_id) that returns any of the above.
+--- <pre>
+--- vim.lsp.handlers["textDocument/publishDiagnostics"] = vim.lsp.with(
+---   vim.lsp.diagnostic.on_publish_diagnostics, {
+---     -- Enable underline, use default values
+---     underline = true,
+---     -- Enable virtual text, override spacing to 4
+---     virtual_text = {
+---       spacing = 4,
+---     },
+---     -- Use a function to dynamically turn signs off
+---     -- and on, using buffer local variables
+---     signs = function(bufnr, client_id)
+---       return vim.bo[bufnr].show_signs == false
+---     end,
+---     -- Disable a feature
+---     update_in_insert = false,
+---   }
+--- )
+--- </pre>
+---
+---@param config table Configuration table.
+---     - underline:        (default=true)
+---         - Apply underlines to diagnostics.
+---         - See |vim.lsp.diagnostic.set_underline()|
+---     - virtual_text:     (default=true)
+---         - Apply virtual text to line endings.
+---         - See |vim.lsp.diagnostic.set_virtual_text()|
+---     - signs:            (default=true)
+---         - Apply signs for diagnostics.
+---         - See |vim.lsp.diagnostic.set_signs()|
+---     - update_in_insert: (default=false)
+---         - Update diagnostics in InsertMode or wait until InsertLeave
+function M.on_publish_diagnostics(_, _, params, client_id, _, config)
+  local uri = params.uri
+  local bufnr = vim.uri_to_bufnr(uri)
+
+  if not bufnr then
+    return
+  end
+
+  local diagnostics = params.diagnostics
+
+  -- Always save the diagnostics, even if the buf is not loaded.
+  -- Language servers may report compile or build errors via diagnostics
+  -- Users should be able to find these, even if they're in files which
+  -- are not loaded.
+  M.save(diagnostics, bufnr, client_id)
+
+  -- Unloaded buffers should not handle diagnostics.
+  --    When the buffer is loaded, we'll call on_attach, which sends textDocument/didOpen.
+  --    This should trigger another publish of the diagnostics.
+  --
+  -- In particular, this stops a ton of spam when first starting a server for current
+  -- unloaded buffers.
+  if not api.nvim_buf_is_loaded(bufnr) then
+    return
+  end
+
+  M.display(diagnostics, bufnr, client_id, config)
+end
+
+--@private
+--- Display diagnostics for the buffer, given a configuration.
+function M.display(diagnostics, bufnr, client_id, config)
+  config = vim.lsp._with_extend('vim.lsp.diagnostic.on_publish_diagnostics', {
+    signs = true,
+    underline = true,
+    virtual_text = true,
+    update_in_insert = false,
+  }, config)
+
+  if diagnostics == nil then
+    diagnostics = M.get(bufnr, client_id)
+  end
+
+  -- TODO(tjdevries): Consider how we can make this a "standardized" kind of thing for |lsp-handlers|.
+  --    It seems like we would probably want to do this more often as we expose more of them.
+  --    It provides a very nice functional interface for people to override configuration.
+  local resolve_optional_value = function(option)
+    local enabled_val = {}
+
+    if not option then
+      return false
+    elseif option == true then
+      return enabled_val
+    elseif type(option) == 'function' then
+      local val = option(bufnr, client_id)
+      if val == true then
+        return enabled_val
+      else
+        return val
+      end
+    elseif type(option) == 'table' then
+      return option
+    else
+      error("Unexpected option type: " .. vim.inspect(option))
+    end
+  end
+
+  if resolve_optional_value(config.update_in_insert) then
+    M._clear_scheduled_display(bufnr, client_id)
+  else
+    local mode = vim.api.nvim_get_mode()
+
+    if string.sub(mode.mode, 1, 1) == 'i' then
+      M._schedule_display(bufnr, client_id, config)
+      return
+    end
+  end
+
+  M.clear(bufnr, client_id)
+
+  diagnostics = diagnostics or diagnostic_cache[bufnr][client_id]
+
+  if not diagnostics or vim.tbl_isempty(diagnostics) then
+    return
+  end
+
+  local underline_opts = resolve_optional_value(config.underline)
+  if underline_opts then
+    M.set_underline(diagnostics, bufnr, client_id, nil, underline_opts)
+  end
+
+  local virtual_text_opts = resolve_optional_value(config.virtual_text)
+  if virtual_text_opts then
+    M.set_virtual_text(diagnostics, bufnr, client_id, nil, virtual_text_opts)
+  end
+
+  local signs_opts = resolve_optional_value(config.signs)
+  if signs_opts then
+    M.set_signs(diagnostics, bufnr, client_id, nil, signs_opts)
+  end
+
+  vim.api.nvim_command("doautocmd User LspDiagnosticsChanged")
+end
+-- }}}
+-- Diagnostic User Functions {{{
+
+--- Open a floating window with the diagnostics from {line_nr}
+---
+--- The floating window can be customized with the following highlight groups:
+--- <pre>
+--- LspDiagnosticsFloatingError
+--- LspDiagnosticsFloatingWarning
+--- LspDiagnosticsFloatingInformation
+--- LspDiagnosticsFloatingHint
+--- </pre>
+---@param opts table Configuration table
+---     - show_header (boolean, default true): Show "Diagnostics:" header.
+---@param bufnr number The buffer number
+---@param line_nr number The line number
+---@param client_id number|nil the client id
+---@return {popup_bufnr, win_id}
+function M.show_line_diagnostics(opts, bufnr, line_nr, client_id)
+  opts = opts or {}
+  opts.severity_sort = if_nil(opts.severity_sort, true)
+
+  local show_header = if_nil(opts.show_header, true)
+
+  bufnr = bufnr or 0
+  line_nr = line_nr or (vim.api.nvim_win_get_cursor(0)[1] - 1)
+
+  local lines = {}
+  local highlights = {}
+  if show_header then
+    table.insert(lines, "Diagnostics:")
+    table.insert(highlights, {0, "Bold"})
+  end
+
+  local line_diagnostics = M.get_line_diagnostics(bufnr, line_nr, opts, client_id)
+  if vim.tbl_isempty(line_diagnostics) then return end
+
+  for i, diagnostic in ipairs(line_diagnostics) do
+    local prefix = string.format("%d. ", i)
+    local hiname = M._get_floating_severity_highlight_name(diagnostic.severity)
+    assert(hiname, 'unknown severity: ' .. tostring(diagnostic.severity))
+
+    local message_lines = vim.split(diagnostic.message, '\n', true)
+    table.insert(lines, prefix..message_lines[1])
+    table.insert(highlights, {#prefix + 1, hiname})
+    for j = 2, #message_lines do
+      table.insert(lines, message_lines[j])
+      table.insert(highlights, {0, hiname})
+    end
+  end
+
+  local popup_bufnr, winnr = util.open_floating_preview(lines, 'plaintext')
+  for i, hi in ipairs(highlights) do
+    local prefixlen, hiname = unpack(hi)
+    -- Start highlight after the prefix
+    api.nvim_buf_add_highlight(popup_bufnr, -1, hiname, i-1, prefixlen, -1)
+  end
+
+  return popup_bufnr, winnr
+end
+
+local loclist_type_map = {
+  [DiagnosticSeverity.Error] = 'E',
+  [DiagnosticSeverity.Warning] = 'W',
+  [DiagnosticSeverity.Information] = 'I',
+  [DiagnosticSeverity.Hint] = 'I',
+}
+
+--- Sets the location list
+---@param opts table|nil Configuration table. Keys:
+---         - {open_loclist}: (boolean, default true)
+---             - Open loclist after set
+---         - {client_id}: (number)
+---             - If nil, will consider all clients attached to buffer.
+---         - {severity}: (DiagnosticSeverity)
+---             - Exclusive severity to consider. Overrides {severity_limit}
+---         - {severity_limit}: (DiagnosticSeverity)
+---             - Limit severity of diagnostics found. E.g. "Warning" means { "Error", "Warning" } will be valid.
+function M.set_loclist(opts)
+  opts = opts or {}
+
+  local open_loclist = if_nil(opts.open_loclist, true)
+
+  local bufnr = vim.api.nvim_get_current_buf()
+  local buffer_diags = M.get(bufnr, opts.client_id)
+
+  local severity = to_severity(opts.severity)
+  local severity_limit = to_severity(opts.severity_limit)
+
+  local items = {}
+  local insert_diag = function(diag)
+    if severity then
+      -- Handle missing severities
+      if not diag.severity then
+        return
+      end
+
+      if severity ~= diag.severity then
+        return
+      end
+    elseif severity_limit then
+      if not diag.severity then
+        return
+      end
+
+      if severity_limit < diag.severity then
+        return
+      end
+    end
+
+    local pos = diag.range.start
+    local row = pos.line
+    local col = util.character_offset(bufnr, row, pos.character)
+
+    local line = (api.nvim_buf_get_lines(bufnr, row, row + 1, false) or {""})[1]
+
+    table.insert(items, {
+      bufnr = bufnr,
+      lnum = row + 1,
+      col = col + 1,
+      text = line .. " | " .. diag.message,
+      type = loclist_type_map[diag.severity or DiagnosticSeverity.Error] or 'E',
+    })
+  end
+
+  for _, diag in ipairs(buffer_diags) do
+    insert_diag(diag)
+  end
+
+  table.sort(items, function(a, b) return a.lnum < b.lnum end)
+
+  util.set_loclist(items)
+  if open_loclist then
+    vim.cmd [[lopen]]
+  end
+end
+-- }}}
+
+return M
diff --git a/runtime/lua/vim/lsp/handlers.lua b/runtime/lua/vim/lsp/handlers.lua
new file mode 100644
index 0000000000..e034923afb
--- /dev/null
+++ b/runtime/lua/vim/lsp/handlers.lua
@@ -0,0 +1,310 @@
+local log = require 'vim.lsp.log'
+local protocol = require 'vim.lsp.protocol'
+local util = require 'vim.lsp.util'
+local vim = vim
+local api = vim.api
+local buf = require 'vim.lsp.buf'
+
+local M = {}
+
+-- FIXME: DOC: Expose in vimdocs
+
+--@private
+--- Writes to error buffer.
+--@param ... (table of strings) Will be concatenated before being written
+local function err_message(...)
+  api.nvim_err_writeln(table.concat(vim.tbl_flatten{...}))
+  api.nvim_command("redraw")
+end
+
+--@see https://microsoft.github.io/language-server-protocol/specifications/specification-current/#workspace_executeCommand
+M['workspace/executeCommand'] = function(err, _)
+  if err then
+    error("Could not execute code action: "..err.message)
+  end
+end
+
+--@see https://microsoft.github.io/language-server-protocol/specifications/specification-current/#textDocument_codeAction
+M['textDocument/codeAction'] = function(_, _, actions)
+  if actions == nil or vim.tbl_isempty(actions) then
+    print("No code actions available")
+    return
+  end
+
+  local option_strings = {"Code Actions:"}
+  for i, action in ipairs(actions) do
+    local title = action.title:gsub('\r\n', '\\r\\n')
+    title = title:gsub('\n', '\\n')
+    table.insert(option_strings, string.format("%d. %s", i, title))
+  end
+
+  local choice = vim.fn.inputlist(option_strings)
+  if choice < 1 or choice > #actions then
+    return
+  end
+  local action_chosen = actions[choice]
+  -- textDocument/codeAction can return either Command[] or CodeAction[].
+  -- If it is a CodeAction, it can have either an edit, a command or both.
+  -- Edits should be executed first
+  if action_chosen.edit or type(action_chosen.command) == "table" then
+    if action_chosen.edit then
+      util.apply_workspace_edit(action_chosen.edit)
+    end
+    if type(action_chosen.command) == "table" then
+      buf.execute_command(action_chosen.command)
+    end
+  else
+    buf.execute_command(action_chosen)
+  end
+end
+
+--@see https://microsoft.github.io/language-server-protocol/specifications/specification-current/#workspace_applyEdit
+M['workspace/applyEdit'] = function(_, _, workspace_edit)
+  if not workspace_edit then return end
+  -- TODO(ashkan) Do something more with label?
+  if workspace_edit.label then
+    print("Workspace edit", workspace_edit.label)
+  end
+  local status, result = pcall(util.apply_workspace_edit, workspace_edit.edit)
+  return {
+    applied = status;
+    failureReason = result;
+  }
+end
+
+M['textDocument/publishDiagnostics'] = function(...)
+  return require('vim.lsp.diagnostic').on_publish_diagnostics(...)
+end
+
+--@see https://microsoft.github.io/language-server-protocol/specifications/specification-current/#textDocument_references
+M['textDocument/references'] = function(_, _, result)
+  if not result then return end
+  util.set_qflist(util.locations_to_items(result))
+  api.nvim_command("copen")
+  api.nvim_command("wincmd p")
+end
+
+--@private
+--- Prints given list of symbols to the quickfix list.
+--@param _ (not used)
+--@param _ (not used)
+--@param result (list of Symbols) LSP method name
+--@param result (table) result of LSP method; a location or a list of locations.
+---(`textDocument/definition` can return `Location` or `Location[]`
+local symbol_handler = function(_, _, result, _, bufnr)
+  if not result or vim.tbl_isempty(result) then return end
+
+  util.set_qflist(util.symbols_to_items(result, bufnr))
+  api.nvim_command("copen")
+  api.nvim_command("wincmd p")
+end
+--@see https://microsoft.github.io/language-server-protocol/specifications/specification-current/#textDocument_documentSymbol
+M['textDocument/documentSymbol'] = symbol_handler
+--@see https://microsoft.github.io/language-server-protocol/specifications/specification-current/#workspace_symbol
+M['workspace/symbol'] = symbol_handler
+
+--@see https://microsoft.github.io/language-server-protocol/specifications/specification-current/#textDocument_rename
+M['textDocument/rename'] = function(_, _, result)
+  if not result then return end
+  util.apply_workspace_edit(result)
+end
+
+--@see https://microsoft.github.io/language-server-protocol/specifications/specification-current/#textDocument_rangeFormatting
+M['textDocument/rangeFormatting'] = function(_, _, result)
+  if not result then return end
+  util.apply_text_edits(result)
+end
+
+--@see https://microsoft.github.io/language-server-protocol/specifications/specification-current/#textDocument_formatting
+M['textDocument/formatting'] = function(_, _, result)
+  if not result then return end
+  util.apply_text_edits(result)
+end
+
+--@see https://microsoft.github.io/language-server-protocol/specifications/specification-current/#textDocument_completion
+M['textDocument/completion'] = function(_, _, result)
+  if vim.tbl_isempty(result or {}) then return end
+  local row, col = unpack(api.nvim_win_get_cursor(0))
+  local line = assert(api.nvim_buf_get_lines(0, row-1, row, false)[1])
+  local line_to_cursor = line:sub(col+1)
+  local textMatch = vim.fn.match(line_to_cursor, '\\k*$')
+  local prefix = line_to_cursor:sub(textMatch+1)
+
+  local matches = util.text_document_completion_list_to_complete_items(result, prefix)
+  vim.fn.complete(textMatch+1, matches)
+end
+
+--@see https://microsoft.github.io/language-server-protocol/specifications/specification-current/#textDocument_hover
+M['textDocument/hover'] = function(_, method, result)
+  util.focusable_float(method, function()
+    if not (result and result.contents) then
+      -- return { 'No information available' }
+      return
+    end
+    local markdown_lines = util.convert_input_to_markdown_lines(result.contents)
+    markdown_lines = util.trim_empty_lines(markdown_lines)
+    if vim.tbl_isempty(markdown_lines) then
+      -- return { 'No information available' }
+      return
+    end
+    local bufnr, winnr = util.fancy_floating_markdown(markdown_lines, {
+      pad_left = 1; pad_right = 1;
+    })
+    util.close_preview_autocmd({"CursorMoved", "BufHidden", "InsertCharPre"}, winnr)
+    return bufnr, winnr
+  end)
+end
+
+--@private
+--- Jumps to a location. Used as a handler for multiple LSP methods.
+--@param _ (not used)
+--@param method (string) LSP method name
+--@param result (table) result of LSP method; a location or a list of locations.
+---(`textDocument/definition` can return `Location` or `Location[]`
+local function location_handler(_, method, result)
+  if result == nil or vim.tbl_isempty(result) then
+    local _ = log.info() and log.info(method, 'No location found')
+    return nil
+  end
+
+  -- textDocument/definition can return Location or Location[]
+  -- https://microsoft.github.io/language-server-protocol/specifications/specification-current/#textDocument_definition
+
+  if vim.tbl_islist(result) then
+    util.jump_to_location(result[1])
+
+    if #result > 1 then
+      util.set_qflist(util.locations_to_items(result))
+      api.nvim_command("copen")
+      api.nvim_command("wincmd p")
+    end
+  else
+    util.jump_to_location(result)
+  end
+end
+
+--@see https://microsoft.github.io/language-server-protocol/specifications/specification-current/#textDocument_declaration
+M['textDocument/declaration'] = location_handler
+--@see https://microsoft.github.io/language-server-protocol/specifications/specification-current/#textDocument_definition
+M['textDocument/definition'] = location_handler
+--@see https://microsoft.github.io/language-server-protocol/specifications/specification-current/#textDocument_typeDefinition
+M['textDocument/typeDefinition'] = location_handler
+--@see https://microsoft.github.io/language-server-protocol/specifications/specification-current/#textDocument_implementation
+M['textDocument/implementation'] = location_handler
+
+--@see https://microsoft.github.io/language-server-protocol/specifications/specification-current/#textDocument_signatureHelp
+M['textDocument/signatureHelp'] = function(_, method, result)
+  -- When use `autocmd CompleteDone <silent><buffer> lua vim.lsp.buf.signature_help()` to call signatureHelp handler
+  -- If the completion item doesn't have signatures It will make noise. Change to use `print` that can use `<silent>` to ignore
+  if not (result and result.signatures and result.signatures[1]) then
+    print('No signature help available')
+    return
+  end
+  local lines = util.convert_signature_help_to_markdown_lines(result)
+  lines = util.trim_empty_lines(lines)
+  if vim.tbl_isempty(lines) then
+    print('No signature help available')
+    return
+  end
+  util.focusable_preview(method, function()
+    return lines, util.try_trim_markdown_code_blocks(lines)
+  end)
+end
+
+--@see https://microsoft.github.io/language-server-protocol/specifications/specification-current/#textDocument_documentHighlight
+M['textDocument/documentHighlight'] = function(_, _, result, _)
+  if not result then return end
+  local bufnr = api.nvim_get_current_buf()
+  util.buf_highlight_references(bufnr, result)
+end
+
+--@private
+---
+--- Displays call hierarchy in the quickfix window.
+---
+--@param direction `"from"` for incoming calls and `"to"` for outgoing calls
+--@returns `CallHierarchyIncomingCall[]` if {direction} is `"from"`,
+--@returns `CallHierarchyOutgoingCall[]` if {direction} is `"to"`,
+local make_call_hierarchy_handler = function(direction)
+  return function(_, _, result)
+    if not result then return end
+    local items = {}
+    for _, call_hierarchy_call in pairs(result) do
+      local call_hierarchy_item = call_hierarchy_call[direction]
+      for _, range in pairs(call_hierarchy_call.fromRanges) do
+        table.insert(items, {
+          filename = assert(vim.uri_to_fname(call_hierarchy_item.uri)),
+          text = call_hierarchy_item.name,
+          lnum = range.start.line + 1,
+          col = range.start.character + 1,
+        })
+      end
+    end
+    util.set_qflist(items)
+    api.nvim_command("copen")
+    api.nvim_command("wincmd p")
+  end
+end
+
+--@see https://microsoft.github.io/language-server-protocol/specifications/specification-current/#callHierarchy/incomingCalls
+M['callHierarchy/incomingCalls'] = make_call_hierarchy_handler('from')
+
+--@see https://microsoft.github.io/language-server-protocol/specifications/specification-current/#callHierarchy/outgoingCalls
+M['callHierarchy/outgoingCalls'] = make_call_hierarchy_handler('to')
+
+--@see https://microsoft.github.io/language-server-protocol/specifications/specification-current/#window/logMessage
+M['window/logMessage'] = function(_, _, result, client_id)
+  local message_type = result.type
+  local message = result.message
+  local client = vim.lsp.get_client_by_id(client_id)
+  local client_name = client and client.name or string.format("id=%d", client_id)
+  if not client then
+    err_message("LSP[", client_name, "] client has shut down after sending the message")
+  end
+  if message_type == protocol.MessageType.Error then
+    log.error(message)
+  elseif message_type == protocol.MessageType.Warning then
+    log.warn(message)
+  elseif message_type == protocol.MessageType.Info then
+    log.info(message)
+  else
+    log.debug(message)
+  end
+  return result
+end
+
+--@see https://microsoft.github.io/language-server-protocol/specifications/specification-current/#window/showMessage
+M['window/showMessage'] = function(_, _, result, client_id)
+  local message_type = result.type
+  local message = result.message
+  local client = vim.lsp.get_client_by_id(client_id)
+  local client_name = client and client.name or string.format("id=%d", client_id)
+  if not client then
+    err_message("LSP[", client_name, "] client has shut down after sending the message")
+  end
+  if message_type == protocol.MessageType.Error then
+    err_message("LSP[", client_name, "] ", message)
+  else
+    local message_type_name = protocol.MessageType[message_type]
+    api.nvim_out_write(string.format("LSP[%s][%s] %s\n", client_name, message_type_name, message))
+  end
+  return result
+end
+
+-- Add boilerplate error validation and logging for all of these.
+for k, fn in pairs(M) do
+  M[k] = function(err, method, params, client_id, bufnr, config)
+    local _ = log.debug() and log.debug('default_handler', method, {
+      params = params, client_id = client_id, err = err, bufnr = bufnr, config = config
+    })
+
+    if err then
+      error(tostring(err))
+    end
+
+    return fn(err, method, params, client_id, bufnr, config)
+  end
+end
+
+return M
+-- vim:sw=2 ts=2 et
diff --git a/runtime/lua/vim/lsp/protocol.lua b/runtime/lua/vim/lsp/protocol.lua
index 70862320c5..07b4e8b926 100644
--- a/runtime/lua/vim/lsp/protocol.lua
+++ b/runtime/lua/vim/lsp/protocol.lua
@@ -1,17 +1,8 @@
 -- Protocol for the Microsoft Language Server Protocol (mslsp)
 
-local protocol = {}
-
---@private
---- Returns {a} if it is not nil, otherwise returns {b}.
----
---@param a
---@param b
-local function ifnil(a, b)
-  if a == nil then return b end
-  return a
-end
+local if_nil = vim.F.if_nil
 
+local protocol = {}
 
 --[=[
 --@private
@@ -909,12 +900,12 @@ function protocol.resolve_capabilities(server_capabilities)
       }
     elseif type(textDocumentSync) == 'table' then
       text_document_sync_properties = {
-        text_document_open_close = ifnil(textDocumentSync.openClose, false);
-        text_document_did_change = ifnil(textDocumentSync.change, TextDocumentSyncKind.None);
-        text_document_will_save = ifnil(textDocumentSync.willSave, false);
-        text_document_will_save_wait_until = ifnil(textDocumentSync.willSaveWaitUntil, false);
-        text_document_save = ifnil(textDocumentSync.save, false);
-        text_document_save_include_text = ifnil(type(textDocumentSync.save) == 'table'
+        text_document_open_close = if_nil(textDocumentSync.openClose, false);
+        text_document_did_change = if_nil(textDocumentSync.change, TextDocumentSyncKind.None);
+        text_document_will_save = if_nil(textDocumentSync.willSave, false);
+        text_document_will_save_wait_until = if_nil(textDocumentSync.willSaveWaitUntil, false);
+        text_document_save = if_nil(textDocumentSync.save, false);
+        text_document_save_include_text = if_nil(type(textDocumentSync.save) == 'table'
                                                 and textDocumentSync.save.includeText, false);
       }
     else
diff --git a/runtime/lua/vim/lsp/rpc.lua b/runtime/lua/vim/lsp/rpc.lua
index 17c411f952..bbcc8ea6f9 100644
--- a/runtime/lua/vim/lsp/rpc.lua
+++ b/runtime/lua/vim/lsp/rpc.lua
@@ -231,41 +231,42 @@ local function rpc_response_error(code, message, data)
   })
 end
 
-local default_handlers = {}
+local default_dispatchers = {}
+
 --@private
---- Default handler for notifications sent to an LSP server.
+--- Default dispatcher for notifications sent to an LSP server.
 ---
 --@param method (string) The invoked LSP method
 --@param params (table): Parameters for the invoked LSP method
-function default_handlers.notification(method, params)
+function default_dispatchers.notification(method, params)
   local _ = log.debug() and log.debug('notification', method, params)
 end
 --@private
---- Default handler for requests sent to an LSP server.
+--- Default dispatcher for requests sent to an LSP server.
 ---
 --@param method (string) The invoked LSP method
 --@param params (table): Parameters for the invoked LSP method
 --@returns `nil` and `vim.lsp.protocol.ErrorCodes.MethodNotFound`.
-function default_handlers.server_request(method, params)
+function default_dispatchers.server_request(method, params)
   local _ = log.debug() and log.debug('server_request', method, params)
   return nil, rpc_response_error(protocol.ErrorCodes.MethodNotFound)
 end
 --@private
---- Default handler for when a client exits.
+--- Default dispatcher for when a client exits.
 ---
 --@param code (number): Exit code
 --@param signal (number): Number describing the signal used to terminate (if
 ---any)
-function default_handlers.on_exit(code, signal)
+function default_dispatchers.on_exit(code, signal)
   local _ = log.info() and log.info("client_exit", { code = code, signal = signal })
 end
 --@private
---- Default handler for client errors.
+--- Default dispatcher for client errors.
 ---
 --@param code (number): Error code
 --@param err (any): Details about the error
 ---any)
-function default_handlers.on_error(code, err)
+function default_dispatchers.on_error(code, err)
   local _ = log.error() and log.error('client_error:', client_errors[code], err)
 end
 
@@ -274,8 +275,8 @@ end
 ---
 --@param cmd (string) Command to start the LSP server.
 --@param cmd_args (table) List of additional string arguments to pass to {cmd}.
---@param handlers (table, optional) Handlers for LSP message types. Valid
----handler names are:
+--@param dispatchers (table, optional) Dispatchers for LSP message types. Valid
+---dispatcher names are:
 --- - `"notification"`
 --- - `"server_request"`
 --- - `"on_error"`
@@ -294,39 +295,39 @@ end
 --- - {pid} (number) The LSP server's PID.
 --- - {handle} A handle for low-level interaction with the LSP server process
 ---   |vim.loop|.
-local function start(cmd, cmd_args, handlers, extra_spawn_params)
+local function start(cmd, cmd_args, dispatchers, extra_spawn_params)
   local _ = log.info() and log.info("Starting RPC client", {cmd = cmd, args = cmd_args, extra = extra_spawn_params})
   validate {
     cmd = { cmd, 's' };
     cmd_args = { cmd_args, 't' };
-    handlers = { handlers, 't', true };
+    dispatchers = { dispatchers, 't', true };
   }
 
   if not (vim.fn.executable(cmd) == 1) then
     error(string.format("The given command %q is not executable.", cmd))
   end
-  if handlers then
-    local user_handlers = handlers
-    handlers = {}
-    for handle_name, default_handler in pairs(default_handlers) do
-      local user_handler = user_handlers[handle_name]
-      if user_handler then
-        if type(user_handler) ~= 'function' then
-          error(string.format("handler.%s must be a function", handle_name))
+  if dispatchers then
+    local user_dispatchers = dispatchers
+    dispatchers = {}
+    for dispatch_name, default_dispatch in pairs(default_dispatchers) do
+      local user_dispatcher = user_dispatchers[dispatch_name]
+      if user_dispatcher then
+        if type(user_dispatcher) ~= 'function' then
+          error(string.format("dispatcher.%s must be a function", dispatch_name))
         end
         -- server_request is wrapped elsewhere.
-        if not (handle_name == 'server_request'
-          or handle_name == 'on_exit') -- TODO this blocks the loop exiting for some reason.
+        if not (dispatch_name == 'server_request'
+          or dispatch_name == 'on_exit') -- TODO this blocks the loop exiting for some reason.
         then
-          user_handler = schedule_wrap(user_handler)
+          user_dispatcher = schedule_wrap(user_dispatcher)
         end
-        handlers[handle_name] = user_handler
+        dispatchers[dispatch_name] = user_dispatcher
       else
-        handlers[handle_name] = default_handler
+        dispatchers[dispatch_name] = default_dispatch
       end
     end
   else
-    handlers = default_handlers
+    dispatchers = default_dispatchers
   end
 
   local stdin = uv.new_pipe(false)
@@ -339,8 +340,7 @@ local function start(cmd, cmd_args, handlers, extra_spawn_params)
   local handle, pid
   do
     --@private
-    --- Callback for |vim.loop.spawn()| Closes all streams and runs the
-    --- `on_exit` handler.
+    --- Callback for |vim.loop.spawn()| Closes all streams and runs the `on_exit` dispatcher.
     --@param code (number) Exit code
     --@param signal (number) Signal that was used to terminate (if any)
     local function onexit(code, signal)
@@ -350,7 +350,7 @@ local function start(cmd, cmd_args, handlers, extra_spawn_params)
       handle:close()
       -- Make sure that message_callbacks can be gc'd.
       message_callbacks = nil
-      handlers.on_exit(code, signal)
+      dispatchers.on_exit(code, signal)
     end
     local spawn_params = {
       args = cmd_args;
@@ -448,7 +448,7 @@ local function start(cmd, cmd_args, handlers, extra_spawn_params)
   local function on_error(errkind, ...)
     assert(client_errors[errkind])
     -- TODO what to do if this fails?
-    pcall(handlers.on_error, errkind, ...)
+    pcall(dispatchers.on_error, errkind, ...)
   end
   --@private
   local function pcall_handler(errkind, status, head, ...)
@@ -471,7 +471,7 @@ local function start(cmd, cmd_args, handlers, extra_spawn_params)
   local function handle_body(body)
     local decoded, err = json_decode(body)
     if not decoded then
-      on_error(client_errors.INVALID_SERVER_JSON, err)
+      -- on_error(client_errors.INVALID_SERVER_JSON, err)
       return
     end
     local _ = log.debug() and log.debug("decoded", decoded)
@@ -484,7 +484,7 @@ local function start(cmd, cmd_args, handlers, extra_spawn_params)
       schedule(function()
         local status, result
         status, result, err = try_call(client_errors.SERVER_REQUEST_HANDLER_ERROR,
-            handlers.server_request, decoded.method, decoded.params)
+            dispatchers.server_request, decoded.method, decoded.params)
         local _ = log.debug() and log.debug("server_request: callback result", { status = status, result = result, err = err })
         if status then
           if not (result or err) then
@@ -551,7 +551,7 @@ local function start(cmd, cmd_args, handlers, extra_spawn_params)
       -- Notification
       decoded.params = convert_NIL(decoded.params)
       try_call(client_errors.NOTIFICATION_HANDLER_ERROR,
-          handlers.notification, decoded.method, decoded.params)
+          dispatchers.notification, decoded.method, decoded.params)
     else
       -- Invalid server message
       on_error(client_errors.INVALID_SERVER_MESSAGE, decoded)
diff --git a/runtime/lua/vim/lsp/util.lua b/runtime/lua/vim/lsp/util.lua
index 9ed19b938d..3deec6d74e 100644
--- a/runtime/lua/vim/lsp/util.lua
+++ b/runtime/lua/vim/lsp/util.lua
@@ -5,50 +5,32 @@ local api = vim.api
 local list_extend = vim.list_extend
 local highlight = require 'vim.highlight'
 
+local npcall = vim.F.npcall
+local split = vim.split
+
+local _warned = {}
+local warn_once = function(message)
+  if not _warned[message] then
+    vim.api.nvim_err_writeln(message)
+    _warned[message] = true
+  end
+end
+
 local M = {}
 
--- FIXME: DOC: Expose in vimdocs
---- Diagnostics received from the server via `textDocument/publishDiagnostics`
--- by buffer.
---
---  {<bufnr>: {diagnostics}}
---
--- This contains only entries for active buffers. Entries for detached buffers
--- are discarded.
---
--- If you override the `textDocument/publishDiagnostic` callback,
--- this will be empty unless you call `buf_diagnostics_save_positions`.
---
---
--- Diagnostic is:
---
--- {
---    range: Range
---    message: string
---    severity?: DiagnosticSeverity
---    code?: number | string
---    source?: string
---    tags?: DiagnosticTag[]
---    relatedInformation?: DiagnosticRelatedInformation[]
--- }
-M.diagnostics_by_buf = {}
+-- TODO(remove-callbacks)
+M.diagnostics_by_buf = setmetatable({}, {
+  __index = function(_, bufnr)
+    warn_once("diagnostics_by_buf is deprecated. Use 'vim.lsp.diagnostic.get'")
+    return vim.lsp.diagnostic.get(bufnr)
+  end
+})
 
-local split = vim.split
 --@private
 local function split_lines(value)
   return split(value, '\n', true)
 end
 
---@private
-local function ok_or_nil(status, ...)
-  if not status then return end
-  return ...
-end
---@private
-local function npcall(fn, ...)
-  return ok_or_nil(pcall(fn, ...))
-end
-
 --- Replaces text in a range with new text.
 ---
 --- CAUTION: Changes in-place!
@@ -121,10 +103,18 @@ local function get_line_byte_from_position(bufnr, position)
   -- When on the first character, we can ignore the difference between byte and
   -- character
   if col > 0 then
+    if not api.nvim_buf_is_loaded(bufnr) then
+      vim.fn.bufload(bufnr)
+    end
+
     local line = position.line
     local lines = api.nvim_buf_get_lines(bufnr, line, line + 1, false)
     if #lines > 0 then
-      return vim.str_byteindex(lines[1], col)
+      local ok, result = pcall(vim.str_byteindex, lines[1], col)
+
+      if ok then
+        return result
+      end
     end
   end
   return col
@@ -700,13 +690,13 @@ end
 
 --- Trims empty lines from input and pad left and right with spaces
 ---
---@param contents table of lines to trim and pad
---@param opts dictionary with optional fields
---             - pad_left   number of columns to pad contents at left (default 1)
---             - pad_right  number of columns to pad contents at right (default 1)
---             - pad_top    number of lines to pad contents at top (default 0)
---             - pad_bottom number of lines to pad contents at bottom (default 0)
---@returns contents table of trimmed and padded lines
+---@param contents table of lines to trim and pad
+---@param opts dictionary with optional fields
+---             - pad_left   number of columns to pad contents at left (default 1)
+---             - pad_right  number of columns to pad contents at right (default 1)
+---             - pad_top    number of lines to pad contents at top (default 0)
+---             - pad_bottom number of lines to pad contents at bottom (default 0)
+---@return contents table of trimmed and padded lines
 function M._trim_and_pad(contents, opts)
   validate {
     contents = { contents, 't' };
@@ -742,19 +732,19 @@ end
 --- regions to improve readability.
 --- The result is shown in a floating preview.
 ---
---@param contents table of lines to show in window
---@param opts dictionary with optional fields
---             - height    of floating window
---             - width     of floating window
---             - wrap_at   character to wrap at for computing height
---             - max_width  maximal width of floating window
---             - max_height maximal height of floating window
---             - pad_left   number of columns to pad contents at left
---             - pad_right  number of columns to pad contents at right
---             - pad_top    number of lines to pad contents at top
---             - pad_bottom number of lines to pad contents at bottom
---             - separator insert separator after code block
---@returns width,height size of float
+---@param contents table of lines to show in window
+---@param opts dictionary with optional fields
+---  - height    of floating window
+---  - width     of floating window
+---  - wrap_at   character to wrap at for computing height
+---  - max_width  maximal width of floating window
+---  - max_height maximal height of floating window
+---  - pad_left   number of columns to pad contents at left
+---  - pad_right  number of columns to pad contents at right
+---  - pad_top    number of lines to pad contents at top
+---  - pad_bottom number of lines to pad contents at bottom
+---  - separator insert separator after code block
+---@returns width,height size of float
 function M.fancy_floating_markdown(contents, opts)
   validate {
     contents = { contents, 't' };
@@ -971,170 +961,80 @@ function M.open_floating_preview(contents, filetype, opts)
   return floating_bufnr, floating_winnr
 end
 
+-- TODO(remove-callbacks)
 do
-  local diagnostic_ns = api.nvim_create_namespace("vim_lsp_diagnostics")
-  local reference_ns = api.nvim_create_namespace("vim_lsp_references")
-  local sign_ns = 'vim_lsp_signs'
-  local underline_highlight_name = "LspDiagnosticsUnderline"
-  vim.cmd(string.format("highlight default %s gui=underline cterm=underline", underline_highlight_name))
-  for kind, _ in pairs(protocol.DiagnosticSeverity) do
-    if type(kind) == 'string' then
-      vim.cmd(string.format("highlight default link %s%s %s", underline_highlight_name, kind, underline_highlight_name))
-    end
+  --@deprecated
+  function M.get_severity_highlight_name(severity)
+    warn_once("vim.lsp.util.get_severity_highlight_name is deprecated.")
+    return vim.lsp.diagnostic._get_severity_highlight_name(severity)
   end
 
-  local severity_highlights = {}
+  --@deprecated
+  function M.buf_clear_diagnostics(bufnr, client_id)
+    warn_once("buf_clear_diagnostics is deprecated. Use vim.lsp.diagnostic.clear")
+    return vim.lsp.diagnostic.clear(bufnr, client_id)
+  end
 
-  local severity_floating_highlights = {}
+  --@deprecated
+  function M.get_line_diagnostics()
+    warn_once("get_line_diagnostics is deprecated. Use vim.lsp.diagnostic.get_line_diagnostics")
 
-  local default_severity_highlight = {
-    [protocol.DiagnosticSeverity.Error] = { guifg = "Red" };
-    [protocol.DiagnosticSeverity.Warning] = { guifg = "Orange" };
-    [protocol.DiagnosticSeverity.Information] = { guifg = "LightBlue" };
-    [protocol.DiagnosticSeverity.Hint] = { guifg = "LightGrey" };
-  }
+    local bufnr = api.nvim_get_current_buf()
+    local line_nr = api.nvim_win_get_cursor(0)[1] - 1
 
-  -- Initialize default severity highlights
-  for severity, hi_info in pairs(default_severity_highlight) do
-    local severity_name = protocol.DiagnosticSeverity[severity]
-    local highlight_name = "LspDiagnostics"..severity_name
-    local floating_highlight_name = highlight_name.."Floating"
-    -- Try to fill in the foreground color with a sane default.
-    local cmd_parts = {"highlight", "default", highlight_name}
-    for k, v in pairs(hi_info) do
-      table.insert(cmd_parts, k.."="..v)
-    end
-    api.nvim_command(table.concat(cmd_parts, ' '))
-    api.nvim_command('highlight link ' .. highlight_name .. 'Sign ' .. highlight_name)
-    api.nvim_command('highlight link ' .. highlight_name .. 'Floating ' .. highlight_name)
-    severity_highlights[severity] = highlight_name
-    severity_floating_highlights[severity] = floating_highlight_name
+    return vim.lsp.diagnostic.get_line_diagnostics(bufnr, line_nr)
   end
 
-  --- Clears diagnostics for a buffer.
-  ---
-  --@param bufnr (number) buffer id
-  function M.buf_clear_diagnostics(bufnr)
-    validate { bufnr = {bufnr, 'n', true} }
-    bufnr = bufnr == 0 and api.nvim_get_current_buf() or bufnr
+  --@deprecated
+  function M.show_line_diagnostics()
+    warn_once("show_line_diagnostics is deprecated. Use vim.lsp.diagnostic.show_line_diagnostics")
 
-    -- clear sign group
-    vim.fn.sign_unplace(sign_ns, {buffer=bufnr})
+    local bufnr = api.nvim_get_current_buf()
+    local line_nr = api.nvim_win_get_cursor(0)[1] - 1
 
-    -- clear virtual text namespace
-    api.nvim_buf_clear_namespace(bufnr, diagnostic_ns, 0, -1)
+    return vim.lsp.diagnostic.show_line_diagnostics(bufnr, line_nr)
   end
 
-  --- Gets the name of a severity's highlight group.
-  ---
-  --@param severity A member of `vim.lsp.protocol.DiagnosticSeverity`
-  --@returns (string) Highlight group name
-  function M.get_severity_highlight_name(severity)
-    return severity_highlights[severity]
+  --@deprecated
+  function M.buf_diagnostics_save_positions(bufnr, diagnostics, client_id)
+    warn_once("buf_diagnostics_save_positions is deprecated. Use vim.lsp.diagnostic.save")
+    return vim.lsp.diagnostic.save(diagnostics, bufnr, client_id)
   end
 
-  --- Gets list of diagnostics for the current line.
-  ---
-  --@returns (table) list of `Diagnostic` tables
-  --@see https://microsoft.github.io/language-server-protocol/specifications/specification-current/#diagnostic
-  function M.get_line_diagnostics()
-    local bufnr = api.nvim_get_current_buf()
-    local linenr = api.nvim_win_get_cursor(0)[1] - 1
-
-    local buffer_diagnostics = M.diagnostics_by_buf[bufnr]
+  --@deprecated
+  function M.buf_diagnostics_get_positions(bufnr, client_id)
+    warn_once("buf_diagnostics_get_positions is deprecated. Use vim.lsp.diagnostic.get")
+    return vim.lsp.diagnostic.get(bufnr, client_id)
+  end
 
-    if not buffer_diagnostics then
-      return {}
-    end
+  --@deprecated
+  function M.buf_diagnostics_underline(bufnr, diagnostics, client_id)
+    warn_once("buf_diagnostics_underline is deprecated. Use 'vim.lsp.diagnostic.set_underline'")
+    return vim.lsp.diagnostic.set_underline(diagnostics, bufnr, client_id)
+  end
 
-    local diagnostics_by_line = M.diagnostics_group_by_line(buffer_diagnostics)
-    return diagnostics_by_line[linenr] or {}
+  --@deprecated
+  function M.buf_diagnostics_virtual_text(bufnr, diagnostics, client_id)
+    warn_once("buf_diagnostics_virtual_text is deprecated. Use 'vim.lsp.diagnostic.set_virtual_text'")
+    return vim.lsp.diagnostic.set_virtual_text(diagnostics, bufnr, client_id)
   end
 
-  --- Displays the diagnostics for the current line in a floating hover
-  --- window.
-  function M.show_line_diagnostics()
-    -- local marks = api.nvim_buf_get_extmarks(bufnr, diagnostic_ns, {line, 0}, {line, -1}, {})
-    -- if #marks == 0 then
-    --   return
-    -- end
-    local lines = {"Diagnostics:"}
-    local highlights = {{0, "Bold"}}
-    local line_diagnostics = M.get_line_diagnostics()
-    if vim.tbl_isempty(line_diagnostics) then return end
-
-    for i, diagnostic in ipairs(line_diagnostics) do
-    -- for i, mark in ipairs(marks) do
-    --   local mark_id = mark[1]
-    --   local diagnostic = buffer_diagnostics[mark_id]
-
-      -- TODO(ashkan) make format configurable?
-      local prefix = string.format("%d. ", i)
-      local hiname = severity_floating_highlights[diagnostic.severity]
-      assert(hiname, 'unknown severity: ' .. tostring(diagnostic.severity))
-      local message_lines = split_lines(diagnostic.message)
-      table.insert(lines, prefix..message_lines[1])
-      table.insert(highlights, {#prefix + 1, hiname})
-      for j = 2, #message_lines do
-        table.insert(lines, message_lines[j])
-        table.insert(highlights, {0, hiname})
-      end
-    end
-    local popup_bufnr, winnr = M.open_floating_preview(lines, 'plaintext')
-    for i, hi in ipairs(highlights) do
-      local prefixlen, hiname = unpack(hi)
-      -- Start highlight after the prefix
-      api.nvim_buf_add_highlight(popup_bufnr, -1, hiname, i-1, prefixlen, -1)
-    end
-    return popup_bufnr, winnr
+  --@deprecated
+  function M.buf_diagnostics_signs(bufnr, diagnostics, client_id)
+    warn_once("buf_diagnostics_signs is deprecated. Use 'vim.lsp.diagnostics.set_signs'")
+    return vim.lsp.diagnostic.set_signs(diagnostics, bufnr, client_id)
   end
 
-  --- Saves diagnostics into vim.lsp.util.diagnostics_by_buf[{bufnr}].
-  ---
-  --@param bufnr (number) buffer id for which the diagnostics are for
-  --@param diagnostics list of `Diagnostic`s received from the LSP server
-  function M.buf_diagnostics_save_positions(bufnr, diagnostics)
-    validate {
-      bufnr = {bufnr, 'n', true};
-      diagnostics = {diagnostics, 't', true};
-    }
-    if not diagnostics then return end
-    bufnr = bufnr == 0 and api.nvim_get_current_buf() or bufnr
-
-    if not M.diagnostics_by_buf[bufnr] then
-      -- Clean up our data when the buffer unloads.
-      api.nvim_buf_attach(bufnr, false, {
-        on_detach = function(b)
-          M.diagnostics_by_buf[b] = nil
-        end
-      })
-    end
-    M.diagnostics_by_buf[bufnr] = diagnostics
+  --@deprecated
+  function M.buf_diagnostics_count(kind, client_id)
+    warn_once("buf_diagnostics_count is deprecated. Use 'vim.lsp.diagnostic.get_count'")
+    return vim.lsp.diagnostic.get_count(vim.api.nvim_get_current_buf(), client_id, kind)
   end
 
-  --- Highlights a list of diagnostics in a buffer by underlining them.
-  ---
-  --@param bufnr (number) buffer id
-  --@param diagnostics (list of `Diagnostic`s)
-  function M.buf_diagnostics_underline(bufnr, diagnostics)
-    for _, diagnostic in ipairs(diagnostics) do
-      local start = diagnostic.range["start"]
-      local finish = diagnostic.range["end"]
-
-      local hlmap = {
-        [protocol.DiagnosticSeverity.Error]='Error',
-        [protocol.DiagnosticSeverity.Warning]='Warning',
-        [protocol.DiagnosticSeverity.Information]='Information',
-        [protocol.DiagnosticSeverity.Hint]='Hint',
-      }
+end
 
-      highlight.range(bufnr, diagnostic_ns,
-        underline_highlight_name..hlmap[diagnostic.severity],
-        {start.line, start.character},
-        {finish.line, finish.character}
-      )
-    end
-  end
+do --[[ References ]]
+  local reference_ns = api.nvim_create_namespace("vim_lsp_references")
 
   --- Removes document highlights from a buffer.
   ---
@@ -1162,109 +1062,6 @@ do
       highlight.range(bufnr, reference_ns, document_highlight_kind[kind], start_pos, end_pos)
     end
   end
-
-  --- Groups a list of diagnostics by line.
-  ---
-  --@param diagnostics (table) list of `Diagnostic`s
-  --@returns (table) dictionary mapping lines to lists of diagnostics valid on
-  ---those lines
-  --@see https://microsoft.github.io/language-server-protocol/specifications/specification-current/#diagnostic
-  function M.diagnostics_group_by_line(diagnostics)
-    if not diagnostics then return end
-    local diagnostics_by_line = {}
-    for _, diagnostic in ipairs(diagnostics) do
-      local start = diagnostic.range.start
-      -- TODO: Are diagnostics only valid for a single line? I don't understand
-      -- why this would be okay otherwise
-      local line_diagnostics = diagnostics_by_line[start.line]
-      if not line_diagnostics then
-        line_diagnostics = {}
-        diagnostics_by_line[start.line] = line_diagnostics
-      end
-      table.insert(line_diagnostics, diagnostic)
-    end
-    return diagnostics_by_line
-  end
-
-  --- Given a list of diagnostics, sets the corresponding virtual text for a
-  --- buffer.
-  ---
-  --@param bufnr buffer id
-  --@param diagnostics (table) list of `Diagnostic`s
-  function M.buf_diagnostics_virtual_text(bufnr, diagnostics)
-    if not diagnostics then
-      return
-    end
-    local buffer_line_diagnostics = M.diagnostics_group_by_line(diagnostics)
-    for line, line_diags in pairs(buffer_line_diagnostics) do
-      local virt_texts = {}
-      for i = 1, #line_diags - 1 do
-        table.insert(virt_texts, {"■", severity_highlights[line_diags[i].severity]})
-      end
-      local last = line_diags[#line_diags]
-      -- TODO(ashkan) use first line instead of subbing 2 spaces?
-      table.insert(virt_texts, {"■ "..last.message:gsub("\r", ""):gsub("\n", "  "), severity_highlights[last.severity]})
-      api.nvim_buf_set_virtual_text(bufnr, diagnostic_ns, line, virt_texts, {})
-    end
-  end
-
-  --- Returns the number of diagnostics of given kind for current buffer.
-  ---
-  --- Useful for showing diagnostic counts in statusline. eg:
-  ---
-  --- <pre>
-  --- function! LspStatus() abort
-  ---     let sl = ''
-  ---     if luaeval('not vim.tbl_isempty(vim.lsp.buf_get_clients(0))')
-  ---         let sl.='%#MyStatuslineLSP#E:'
-  ---         let sl.='%#MyStatuslineLSPErrors#%{luaeval("vim.lsp.util.buf_diagnostics_count([[Error]])")}'
-  ---         let sl.='%#MyStatuslineLSP# W:'
-  ---         let sl.='%#MyStatuslineLSPWarnings#%{luaeval("vim.lsp.util.buf_diagnostics_count([[Warning]])")}'
-  ---     else
-  ---         let sl.='%#MyStatuslineLSPErrors#off'
-  ---     endif
-  ---     return sl
-  --- endfunction
-  --- let &l:statusline = '%#MyStatuslineLSP#LSP '.LspStatus()
-  --- </pre>
-  ---
-  --@param kind Diagnostic severity kind: See |vim.lsp.protocol.DiagnosticSeverity|
-  --@returns Count of diagnostics
-  function M.buf_diagnostics_count(kind)
-    local bufnr = vim.api.nvim_get_current_buf()
-    local diagnostics = M.diagnostics_by_buf[bufnr]
-    if not diagnostics then return end
-    local count = 0
-    for _, diagnostic in pairs(diagnostics) do
-      if protocol.DiagnosticSeverity[kind] == diagnostic.severity then
-        count = count + 1
-      end
-    end
-    return count
-  end
-
-  local diagnostic_severity_map = {
-    [protocol.DiagnosticSeverity.Error] = "LspDiagnosticsErrorSign";
-    [protocol.DiagnosticSeverity.Warning] = "LspDiagnosticsWarningSign";
-    [protocol.DiagnosticSeverity.Information] = "LspDiagnosticsInformationSign";
-    [protocol.DiagnosticSeverity.Hint] = "LspDiagnosticsHintSign";
-  }
-
-  --- Places signs for each diagnostic in the sign column.
-  ---
-  --- Sign characters can be customized with the following commands:
-  ---
-  --- <pre>
-  --- sign define LspDiagnosticsErrorSign text=E texthl=LspDiagnosticsError linehl= numhl=
-  --- sign define LspDiagnosticsWarningSign text=W texthl=LspDiagnosticsWarning linehl= numhl=
-  --- sign define LspDiagnosticsInformationSign text=I texthl=LspDiagnosticsInformation linehl= numhl=
-  --- sign define LspDiagnosticsHintSign text=H texthl=LspDiagnosticsHint linehl= numhl=
-  --- </pre>
-  function M.buf_diagnostics_signs(bufnr, diagnostics)
-    for _, diagnostic in ipairs(diagnostics) do
-      vim.fn.sign_place(0, sign_ns, diagnostic_severity_map[diagnostic.severity], bufnr, {lnum=(diagnostic.range.start.line+1)})
-    end
-  end
 end
 
 local position_sort = sort_by_key(function(v)
@@ -1561,6 +1358,9 @@ function M.character_offset(buf, row, col)
   return str_utfindex(line, col)
 end
 
+M._get_line_byte_from_position = get_line_byte_from_position
+M._warn_once = warn_once
+
 M.buf_versions = {}
 
 return M
diff --git a/runtime/lua/vim/shared.lua b/runtime/lua/vim/shared.lua
index 995c52e8ed..998e04f568 100644
--- a/runtime/lua/vim/shared.lua
+++ b/runtime/lua/vim/shared.lua
@@ -96,7 +96,7 @@ end
 ---
 --- Examples:
 --- <pre>
----  split(":aa::b:", ":")     --> {'','aa','','bb',''}
+---  split(":aa::b:", ":")     --> {'','aa','','b',''}
 ---  split("axaby", "ab?")     --> {'','x','y'}
 ---  split(x*yz*o, "*", true)  --> {'x','yz','o'}
 --- </pre>
@@ -496,7 +496,7 @@ do
   }
 
   local function _is_type(val, t)
-    return t == 'callable' and vim.is_callable(val) or type(val) == t
+    return type(val) == t or (t == 'callable' and vim.is_callable(val))
   end
 
   local function is_valid(opt)